What approach to take?

My main concern here would be that, since I don't know what I 'did/said' to cause such offence then I might just go and repeat the disaster in innocence.

I read the comment the same way as vickymeldrew. Just that you might make the situation or the relationship worse not that there is some particular dragon to be slain. He was just trying to keep things calm and I can't see why he is being criticised. It is his mother and his wife and he doesn't want unnecessary conflict.

I gave each of my 3 children a fairly large sum early this year......one of them doesn't even want to know me now.....even though I am hurt, I will never throw it back in their face......it was a gift and that's it, as far as I am concerned .

Easybee I think the comment about not paying for accommodation when you have helped provide extra for the family is possibly the attitude which could have caused the problem in the first place. It infers that the money was conditional and you think they now can expect certain rights because of it. I gave my dd and sil some money to help with her house, however I would NEVER expect any rights over their house because of it. A gift should be unconditional, if not don’t give it, or it can cause major issues if it is “cast up.”

Go!
The positives outweigh the negatives: you get to see and spend time with the grandchildren and your son; you can admire the extension; you may discover the reason for and deal with IT, and you don't have to organise Christmas.
You appear to be the adults in this scenario, so follow the wise advice for a charm offensive, respond to every negative with a positive, and have suggestions for other activities to leaven the atmosphere, if there is one: treats such as the pantomime, cinema, restaurant, shopping, long walks etc. Four days isn't that long, with children to engage with.
It would seem that as your daughter in law has a difficult relationship with her own mother, the problem stems from her; she may be one who is happy to accept a gift (for extensions) but resents the giver, as seems to be increasingly the expectation on here. I don't blame you for not wanting to pay for accommodation when you have helped provide extra for your family.
As you live in different countries I am assuming that the 'not talking' is via technological communication, phone, emails, skype etc, and she hasn't actually physically refused to speak when you are face to face. Even if she does, there are plenty of other people about to talk through, and you can just put it down to sheer bad manners.

I think IT is a red herring! When DS said “might make it worse”, my reading of that is that it would make the ‘situation ‘ worse, not alluding to any particular problem. If DIL doesn’t get on with her own mother either, then it’s a problem she has with relationships not an unknown incident that has coloured everything else. DIL is just a difficult person. Go along to see them, stay in their home as invited and enjoy the company of GCs. Ignore old frosty knickers!

Firstly, 'phone your son. You have to know what IT is. How can you possibly make amends with your daughter-in-law, if you don't know how you've offended her?
If possible, cut down your visit to two (at most, three) days, and just see how you get on. (Four days is a long time, if things are awkward.)

The fact that dil has bad relationship with own mother says it all - she expects you to be the same as her own mother. Any innocent remark you might make could be interpreted as if it came from her own mother and to her will mean something different (bad) from what you intended. That might be the cause of the not talking for 9 months.

Just go, be nice and bear in ind she is in a difficult place because of her history.

If you haven't seen each other for 9 m9nths, when would you be talking to each other?
My DM and MIL spoke to me/DH on calls.
I spoke to MIL if I picked up phone first only plus she did call me a few times over the yearsas she was fond of me (When DH at work). We didn't pass calls to each other..

Presumably DiL has agreed to the visit! Maybe this is her way of saying " I have been a bit silly"
We are not all perfect and able to do the right thing at the right time in the right way.
Of course ideally DiL would say " I am sorry, I got upset over xxxxx because yyyyy"

Also , to be fair, we only have MiL side of the story.. sorry evaniers I jut mean that your DiL may have a completely different perspective on a situation than you have.

If both now want to keep the relationship as positive as possible stamping of feet or taking umbrage is not going to heal the scar!

Your son is dragging it out and making this situation worse.

His wife is upset for whatever reason, hasn't spoke to her MIL for almost a year, he knows why but won't say, his Mum is in the dark, has no idea why and he then wants to bring her into the house for 4 days with his wife and mum not talking...throw in the most stressful time of year...my god.

You couldn't pay me to walk into that pressure cooker.

Ask your son what's going on and you want the truth.

newnanny
Why are you suggesting that the OP lies down, buys a 'value gift', flowers, admire the house, smile a lot, offer to babysit and generally behave like a doormat when she has absolutely no idea what, if anything, she has done to ruffle her DiL's feathers?
More importantly, her own son won't tell her.
Fancy being put in that position by your own son in order to see your grandchildren.
He should be ashamed and, if it were me, I wouldn't stay in their home under any circumstances. The OP would be under sufferance, having to walk on eggshells, wondering whether any offers of help would be snubbed or if she should not offer and seem 'above it' as she paid towards renovations...it's ridiculous and absolutely out of order to treat visitors in that manner.
Forced jollity at celebrations is a dreadful idea. The OP and her husband have a right to be made comfortable in every sense of the word.

she also has a disastrous relationship with her own mother

This might be the main problem. If she has an up and down relationship with her mother maybe she expects to have one with you so actually ends up engineering one because she's looking for trouble. If that is the case, you may find that she is also used to the relationship going back to normal without clearing the air or trying to resolve the problem.
I'm afraid I would be quite up front with my DIL. I don't expect my AC to have to balance us! I would (and have) written to my DIL and apologise for offending her. I would be quite honest and say that how thrilled I was to be invited but it was playing heavily on my mind that I might upset her again as I wasn't sure what I had done wrong. I would probably say that I would understand if she felt it was too much to entertain me for 4 days and I would not be offended if she felt she would prefer me to give her some peace and quiet at points which could be made possible if you stayed somewhere else for all or some of the time. I'd make sure I told her how much I loved her hospitality but Christmas is a time for her too.

Can I be the daughter in law’s advocate here? My parents in law used to come and stay with us five or six times a year, always staying at least a week. I used to find it a strain, particularly since they didn’t get on with each other, and my father in law was very critical- including of the way I brought up the children. However, I used to put up with it for everyone’s sake. How much easier it would have been if they had just stayed in a hotel and been with us during the day. I hope I was welcoming, but I’ve no doubt I wasn’t always a ray of sunshine. Christmas is the worst time to have visitors. The children are over-excited, there’s a huge burden of expectation, huge hot meals to cook, it gets dark early, and it’s rarely nice enough to get outside. We don’t know what IT is, but maybe, since you have been invited, you could go some way to make it an easier Christmas for everyone.

I would be generous and polite. Buy her a good value gift card for hosting you and offer to help prepare veg etc. Be friendly and smile a lot at her. Tell them both you are delighted to be there. Offer to babysit dgs so they could go out alone as they may not get many chances through year.

We could easily have been in your situation, and indeed have sort of been with her barely speaking to us, and leaving everything connected with us staying to DS, then usually ending up staying in the bedroom half our visit with some feigned illness. After that there were 2 years of her not speaking, and we never saw her again.

However, there have been some really good points made here. If we had been invited we would have gone, offered but not pushed staying elsewhere, certainly not confronted the problem, and tried to be ourselves. While people will say you need to get to the bottom of the situation, with some people it just doesn't work, and in everything yo do you are damned if you do and if you don't. It is usually a good idea to check what presents one is allowed to give the children, and praise the house. Good luck, and if they don't make you feel relaxed, then blame them, and make the most of seeing the children

I think I'd stay in a hotel, too - somewhere to retreat to if the atmosphere should be at all difficult - and to give dil her own space back for a while twice a day.,,
4 nights is a lot, even if you all get on very well.

My sister and bil stay at a nearby hotel when seeing their ds, , dil and gdcs. They get on v well with dil, and they do have room, but it means peace and quiet in the morning, and if/when they're getting tired later.

I think your son needs to put you in the picture. Assure him if he does tell you what the situation is, it will go no further. It’s very unfair of him, if he does know, not to tell you. If you don’t know how do you put things right? He has a duty to you as well as his wife. Either way just go.

So many DIL problems on GN nearly every day some poor soul has a problem.
Sounds as if your sons not to sure about the situation either
Makes you think what’s she putting him through.
Write her a little note or better still send some flowers. I wouldn’t go to there for Christmas if the situation is not better.

It seems that an olive branch has been offered. I would go and try to keep things light and civil.
I agree with janeainsworth about 'thrashing things out' not always making things better. It can end up with some people getting things off their chest and others feeling they've been got at.
Play it by ear but don't be careful that you are not looking for an opportunity to make a point as the situation will still be fragile for a while.
It is the first step. Don't expect too much from it.

As I read all the posts, I agree.....staying at a hotel might be perceived as a snub and actually make things worse.

On the other hand, you need to avoid walking into a potential mine field.

I don't think it's unreasonable to call your son privately (at his place of work?) to let him know how troubled and saddened you are being faced with an issue you can't address because you don't even know what 'IT' is!

Let him know that you are delighted with their invitation, but that you would hate for misunderstandings or sad feelings to interfere with what should be a happy family occasion.

If you refuse the invitation I can only think it will make matters much worse!

In your place, I would tell myself that four days is a very short length of time and that it is worth going to see the family and in the hope that it will improve matters.

I think I would try to be the perfect guest, offer to help, play with the children etc. Don't ask what IT is, until the last day, where I would say thank you for the visit, and perhaps add that I hope that whatever you or your DH said to cause such offence that DIL has refused to speak to you can either be considered a thing of the past, or discussed openly, so you all can move past it.

I am not saying that you and your DH did anything to offend her, but by putting it that way, she is less likely to be so defensive that she refuses to listen to you.

If the four day visit is an unmitigated disaster, I would write my DS a letter once I got home, pointing out that if the family is to be able to function as a family, he really must tell you what all this is about, so you and his wife can work something out.

I'm hoping that she having consented to invite you is going to try to get past this sad business too, or at least tell you why she is or has been in such a huff.

agree totally with Buffebee

Again, I am sorry to appear critical of DS, but boy is he playing with fire here.

You tried to invite yourselves over for a visit in the summer; the strong implication from events is that DIL indicated she would not go along with this; and he is STILL shoving you all together at Christmas whilst he himself is making no effort to mediate the situation or even speak openly about it.

I cannot see how without a significant change in his approach this is going to end well.

And it IS his responsibility to be the one who tries to resolve the situation, as he is the only one still talking to all parties involved and who wants the visit to take place.

You say your daughter in Law hasn't spoken to you for 9 months. Have you spoken to her? Does she realise you haven't spoken for 9 months? Inviting you for Christmas for 4 days is an act of warmth and amiability not in keeping with deep anatgonism. I'd certainly go as you have a son and grandchildren to see. Just send a lovely card to her saying you looking forward and is there anything in particular you can take or do. Also what would the grandchildren like for Christmas.? She can either email/telepphone/text or Whatsapp. Good Luck.