My DD has just turned up on our doorstep...

Just be there for her to give her support and know there is always someone there for her. Also if she wants to talk try to ask her what she wants. Listen to her rather than advise because you don't want her to stop coming to you which she might if you advise something she doesn't like or she thinks you are being too critical. Whatever decison she makes has to be hers and you need to make her confident enough to make the right decision or to come to you if she needs it.
Having said that it must be hard. He sounds terrible and if it were me I am sure I would have trouble biting my tongue.

Support her in any way you can. Yes it would be much better if he left the house, but you do not know what she has been putting up with. There will be something behind it, she is obviously knackered, when she is rested you can find her help, woman's aid perhaps if there is abuse of any kind, a solicitor to find out her rights and get general advice. If she has changed from being a strong woman something has happened for sure. Seeing a solicitor does not mean that she has to instigate divorce proceedings but helps her assess her options. If he is abusive do not at all suggest at she stays with him, encourage her to speak to women's aid. If you need to help her get things get important papers, passports, birth certificates, bank documents, any personal valuables such as jewellery, photos, laptops etc. The fact that he is sitting put is v concerning
Limit what is said about the situation in front of the grandchild, who will already be unsettled.
If you have to say something say it along the lines of I've noticed that he did this, that, has said this, said that.

I'm going through something similar but my dd is 20 and they all living with me, so following for advice because I'm struggling to stay out of it too xx

One question ....why has your daughter and child moved out. If he doesn’t want to be with her anymore surely it’s for him to go back to his family. Your grandchild needs the stability of their own home.Have a word with her...she needs to know her rights in the break-up.

I am wondering right now why you are so sure that "everything will be sorted" ? Your SIL has apparently told his wife he no longer wants to be with her. What does she want?

Ask her, that is after all the first priority.

I don't think you have done harm by saying that you were surprised how critical he was when you stayed with him.

Not knowing why your SIL says he doesn't want her any more, none of us can really advise.

Be there for your daughter but don't interfere or you'll end up being the bad person .

She may need space to work out what she wants to do... all you can do is be there for her but dont offer advice as they have to work it out.
Suggest that you offer to look after GS so they can actially meet up and talk things through

I think there are probably issues going way beyond a "silly" argument and it is probably the proverbial straw. Sometimes a Mum's shoulder is the only thing that helps and so here you are. Just be comforting without judgement and, if it is really over, get her to seek legal advice.
My SIL recently talked to me about leaving my daughter. Whilst I understand many of the problems faced by him (he ain't perfect either) I tried to be supportive but had to point out to him that, when push came to shove, I would have to support my daughter but I would encourage her to be fair and to put the children first before her angst about him. He talked to my son yesterday and he repeated what I'd said so I hope he will remember that if it comes to a break up. He wants custody of the children so I can see it being a free for all and I am not sure I can bear it.

@scentia I don't believe what I'm listening to here, "They just seem so childish and I suppose at 25 they are children." sorry I should explain, I say listen to because, I am BLIND and so, therefore, I must use assistive technology in order to use the computer so it reads out loud to me.
"at 25 they are children" well if she's still a kid at 25 that's YOUR fault. I understand she has a son of her own is that responsible?
Sorry if this is not the answer you wanted but some folk have REAL problems.
Supposing by YOU writing this `attention-seeking` drivel you have made the situation worse? because sure as eggs are eggs someone (his friends and family) has seen this and told him about it.
Bottom line pet "did the world need to know about this? Or is this a private matter?`

There are “silly rows” and many other reasons couples fall out. Sometimes an ongoing “silly row” causes bad behaviour on one or both sides. So, it could be something or nothing.
On the other hand, it could be an ongoing, serious problem.
I would certainly ignore the advice to leap into instant action!
Rushing round and grabbing all her stuff or encouraging her to leave (or reconcile) are not options.
This could be a life changing decision to make or a gradual reconciliation.
When she’s rested and thinking a bit more clearly, it’s a chance to talk and discuss. Just explain things may help. Otherwise, relationship counselling may help clear the air - together or alone.
All you need to do is be the support. Make it clear that you’re there for her whatever happens - don’t lay blame, encourage discussion and help her make her own choice.
She’s got a problem but no one knows how serious that may be yet. Definitely not a time for knee jerk reactions.

Yennifer

He's very very critical of her, your husband doesn't like it but you think it's silly? If he is happy to be like that in front of you, how bad is it behind closed doors?
^
This with bellls on.

What else can you do other than give shelter and comfort to DD and GC. You can't become embroiled in their issues. Sorry but I don't agree about 25 year olds being children. They are adults. SiL does seem very controlling and demeaning. Hope it isn't long until tger is a resolution.

ExD1938 You say, "We all know husbands can be controlling at times (or try to be) but its not a reason to end a marriage." Actually, I think it's a very good reason to end a marriage. Nobody should have to put up with constant criticism. That's just plain bullying and if it's clear to see in public, it might well be worse in private. Would anyone want their children to be raised seeing such lack of respect for their mother? I doubt it. Hope it all works out.

Message withdrawn at poster's request.

Just consider whether there’s an element of coercive control in their relationship. It is often hidden from the wider family of the victim. A ‘silly argument’ might be the straw that breaks the camel’s back. Listen carefully to your daughter and read between the lines.

Isn’t that mental cruelty constantly criticising someone, that must be very soul destroying for her, and her son hearing her being picked on like that day in day out is not good for either of them. If it was my daughter I’d be telling her what I saw and how I felt I couldn’t sit back and watch her be treated like that. We wouldn’t fall out over it tho as she’d take my views on board, just as I did my mums.

It sounds like you’re doing all the right things already. Be there for your daughter and grandson. That’s all you can do. Let them work it out, otherwise you could find yourself being the bad guy.

So your daughter and GS have turned up on your doorstep, obviously very upset, your DD is saying that her OH no longer wants to be with her. Quite frankly, I would be jumping in your car and going to collect her belongings for her!
I don't really understand what your hesitation is - do you believe that the way that your SiL was acting while were together was just for show? My guess is that you had seen what he was like, and chose to ignore it.
You can't understand why your daughter is not the strong woman that you brought her up to be? Believe me, being constantly criticised and run down is like a dripping tap on a bar of soap - it wears away all of your self belief over time, making you turn into half the person you were.
What your daughter needs right now is your love and support in whatever she chooses to do about her marriage. Whether you like it or not, you are involved - this is more than something silly - it may well be the straw that broke the camel's back and for your DD sake I hope it is.
Think of your GS. Do you want him to see the way that his father behaves and to grow up to think that it is the normal way for a man to behave towards a woman ? I certainly wouldn't!

I second exactly what Welbeck said

If he said he doesn’t want to be with her any more then why wasn’t him who moved out?

Did your daughter get thrown out or did she leave of her own accord? The reason I ask is that if this should go to a divorce case then this will be very important as to the financial divide of assets. I think your d would be advised to get some legal help on this one.

if he wants to be on his own, why has she left the house.
he should leave if he wants to be alone.
this could be a much more abusive situation than you realise.
she could contact womens aid for advice.
there may be legal implications if she leaves the house.
it may make asserting her rights more difficult.
big up her autonomy as an adult person, with an expectation of being treated with respect,
and that you will support her to make the best decisions for her and son.
she doesn't have to put up with a lifetime of being spoken down to, criticised, on the defensive, low-level aggression rumbling away, in her own home, with a controlling man.
co-ercive control is also abuse, and now recognised as a criminal offence.
you didn't notice it before, but your husband did; what else is going on ?

This could go either way Scentia. It could be the start of ending the relationship or she/they could decide to give it another go. I would give as much support as possible. Lend a listening ear but be very careful, going forward, about what you say about him. If they do get back together you will remember all the ways she has told you he is awful to her but she will forget/retract and, as others have said, this could damage your relationship going forward. Also make sure you don't speak negatively about her husband in front of your little grandson. It will upset him and he could well repeat anything he hears at a later date with unlooked for consequences.
Good luck op it is sometimes difficult as a mother to grown up 'children' knowing what's best to say and do

Yehbutnobut
Thanks for your input, but she has been in bed since 8.00pm ?

I’d get off GN and talk to her.