How do I get through to her?

You have invited everyone, she has refused, it’s you that needs to respect her wishes. Her decision.
Your sister will be upset at the estrangement, it means not seeing her only son and grandchildren. You don’t know the reasons for the estrangement and shouldn't judge. She is losing out. I would attend if it were me, take any chance to see gc. However I am not her.
Invite her another time or go out with her.

Can I ask why she's estranged with her son? It sounds like she initiated the estrangement, since her son doesn't mind seeing her.

Did no contact happen because the son severely mistreated her grandchildren or maybe unapologetically killed the family dog one drunken night?

Or is this just another form of attempted control over the son? Giving him the silent treatment because he didn't do something she wanted, maybe like spending less time on his nuclear family to spend more time on her?

Does it matter? She sounds like a spoiled brat and your celebrations will be better without her. You can't spend the holiday pussy-footing around divas.

It's a family tradition where everyone is invited. As you said, you can't simply un-invite your nephew and his family just because your sister has had a falling out with them.

I'd tell her that, as always, the invite is open to all, and you wouldn't want anyone to be left out. However, you need to tell her that the issue between her and her son is nothing to do with you, and they need to sort it out between themselves, and decide what they're going to do about it. It's not right that you should be put into a position of having to choose between certain family members. Let them sort it out and decide whether or not they can act like adults, and not create a bad atmosphere, and spoil the day for everyone else. Or, one of them chooses not to come. Their decision, not yours.

And I'd also be telling them that if one or the other causes any upset on the day, then you'll have to ask them both to leave, as it's not fair on everyone else.

Hope it can all be sorted out before Christmas!

You can’t control others feelings or decisions You have invited them now up to them whether they come or not Now it’s OUT of your hands
The trouble with big family get togethers there ll always be someone not doing what you want or expect
Enjoy your meal

I agree with Grams2five, you have done your best and invited everyone.
Your sister, in my opinion, is pitting you against her son which I see as spiteful and childish.
As you say "Next Christmas isn't promised to any of us" and if your sister can't look at the big picture she is missing the whole point of family and Xmas celebrations.
Good luck, sometimes we have to be the adult in the room and look further than the disagreements which pop up in all relationships.

I think you’ve done your part by inviting them both. If nephew and his family are fine coming if she’s there or not then the onus is on your sister to decide what matters more to her. Continuing the estrangement and staying away or coming to the family holiday. It’s her choice to make and no one to blame but herself if she stays away. You’ve invited them both mot taken sides it’s up to the to choose for themselves

Is he actually going to come?

Yes I realize the most likely outcome is that she will likely not come and it will be a shame. Her grandchild will be there. My children are looking forward to seeing her, as two of them live a distance and have a close relationship with her, as I do with her sons. Prior to our most recent conversation, my sister and I saw each other regularly. It’s not just that I won’t see her, but about her being proud and a bit spiteful to kill a tradition our children and their children look forward to each year. We all did. Her son and DIL have no problem with her being there. She should get over herself and put this silly feud aside to be with her family at Christmas. That’s what family is about, being tolerant. Next Christmas isn’t promised to any of us.

The problem with this is that other family members could be drawn into this estrangement making this a much bigger issue with some taking sides.
I know is a tradition but will still be a family bash if your sister isn’t there but can arrange to see you another day, surely this can happen if someone falls ill. And would only suggest that your nephew and family come because if they have children that is what Xmas is all about.
And if your sister is upset about this, indeed I imagine she is upset already about the estrangement so maybe Xmas isn’t that important to her right now, just tell her that in the circumstances you had no choice but will really miss her on the day as will other family members and look forward to seeing her Xmas eve/boxing day.
Can’t really see how you can do this otherwise.

keepingquiet

She is 'threatening' not to show up for a family celebration. I don't understand why not showing up would be a threat to you?
It may be disappointing and hurtful, but a threat?

You then say she and her family are estranged- from each other, or from you? Again, I'm confused.

I read on, and figure that because you have invited her son, from whom she is estranged, she won't come.
I think I would be inclined to say that you are free to invite who you like, and if she doesn't want to be there, then that's her choice.

I'm sorry she is putting you through this- could you maybe ask her to come another time, when she feels comfortable doing so?

We have a sister like this, but we tend to ignore her drama making and carry on regardless. Maybe have a word with your nephew too? Why would he come if he knew it would upset his mum?

I think this is something they have to work out between themselves so maybe don't invite either of them until they can behave like adults. You don't need this kind of stress in your life. Leave them to it.

This is a tradition we have kept since our parents died. It’s not a small matter if she doesn’t show. Everyone will be upset to see the division. My sister and her son are estranged but they are equally entitled to attend this particular family event. It’s not my place to decide who is and isn’t invited, I can only decline to host. The family would like us all to continue. My sister is the only person making an issue.

flappergirl

So were your sister and her son not estranged last Christmas? What were the arrangements then?

They were not but the tension was palpable.

She is 'threatening' not to show up for a family celebration. I don't understand why not showing up would be a threat to you?
It may be disappointing and hurtful, but a threat?

You then say she and her family are estranged- from each other, or from you? Again, I'm confused.

I read on, and figure that because you have invited her son, from whom she is estranged, she won't come.
I think I would be inclined to say that you are free to invite who you like, and if she doesn't want to be there, then that's her choice.

I'm sorry she is putting you through this- could you maybe ask her to come another time, when she feels comfortable doing so?

We have a sister like this, but we tend to ignore her drama making and carry on regardless. Maybe have a word with your nephew too? Why would he come if he knew it would upset his mum?

I think this is something they have to work out between themselves so maybe don't invite either of them until they can behave like adults. You don't need this kind of stress in your life. Leave them to it.

So were your sister and her son not estranged last Christmas? What were the arrangements then?