To think DH is insane to suggest this

Because exes like this weaponise their children to get their own way. It's the turn of their father to have them for Christmas dinner, she should honour that arrangement.

I totally agree with you OP.

The original arrangements should stand.

It's unfortunate her relationship has ended but I don't see why it gives her the right to start changing things just to suit her.

I think your DH's reaction was very hurtful. Hopefully it was a heat of the moment reaction and when he has calmed down you can have a reasonable conversation.

I don't see why he should be happy to spoil your Christmas and your DD's Christmas just to accommodate a totally unreasonable demand by his ex.

Does DC often hang out at XW’s home? Is this a familiar environment?

If he didn't give a shit about their shared DC, he wouldn't be proposing to bring her and all her three year old chaos with him.

Doesn't work like that - she's only just split with her DP and is likely raw. You haven't

Maybe it’s an excuse and the teenagers don’t want to split the day this year 😕

God your standards are low.

Man agrees to something he doesn't want.

Man then expects woman to do something she doesn't want, because he fucked up.

Man is being dismissive of shared child together, her importance and her needs.

You: it's fineeee, he's sooo great, just have a bath!

I think your husband should be kind and allow a one off (and make it clear that it is a one off) that his ex has the children all Christmas Day this year.
Insist that you have the DSC over for an evening meal on Christmas Eve and to open presents and that they come back again for Boxing Day afternoon.

Alternatively, your DH should just say NO to his ex but you both could extend an invitation to her to spend the middle of Christmas Day and have lunch at your home (again as a one off).

If could be a new way that offers your DSC a serene day where their parents can be civil in the same space for an hour or two. Good practice for when they graduate or get married.

If the arrangements for Christmas have been formally agreed then he should insist that they come to you, if she's on her own that's tough but not your problem.

It's not a compromise when only one person gets what they want, and everyone else is bending backwards to accommodate it.

What is the ex compromising?

Personally I’d be really impressed your husband is kind with high EQ.

I’d plan to do something for for those 2 hours in the afternoon while he goes to her house. Have a bath, watch a film, have a nap! Do some nice cooking. Anything, read a book.

I think you are wanting to be stubborn for all the wrong reasons

Completely agree.
I find it worrying that a parent would be using their own children as an emotional crutch because their relationship has broken down. Especially when they seemingly agreed to the ‘sharing’ of the children previously.
I would expect my partner to protect his kids by making sure their mother’s relationship status has no effect on them.

Makes you wonder who are the adults and who are the children here.
Christmas goes on as normal. Ex thinks she’ll be sad because she’ll be alone half the day? Tough. You suck it up and smile for the kids sake.
Been there , done that for several Christmasses. She puts her feet up, watches a movie.
Don’t try to make it artificially cheerful shoving you all together or what is really weird taking your 3 year old to ex’s house.
Time your HH and his ex grew up.

Did you miss this part of the OP?

I need to add that they have not always gotten along, DH and ex. There were some really awful times, abusive messages, difficulties agreeing to contact schedules, being awful about me etc... I rarely say more than the odd hello to her.

This is the most sensible solution.
Your DH also owes you an apology

Why does the place the ex is in have to negatively affect OP’s Christmas Day? She’s out of order to change the plans one-sidedly

I think if the kids are teens they can vote with their feet surely? Ask them if they want the usual split or would rather spend the full day with mum and see you Boxing Day.

chances are they find changing places mid day disruptive and would probably prefer to stay in one place.

Seems like a solution where the ex gets what she wants.

see it would see it as a compromise. And a dare say if you are in a ‘blended’ family a level of compromise is needed. I get it if the SC mum is a nightmare all the time but if the friction and difficulty has been both ways, which is more often is, I would try and be accommodating. Keep the visit short, use the time for yourself or to prep for your family coming.

Her relationship ended. Her problem. The arrangements for the DSC shouldn't change because of that.

Let him take your child over in the afternoon for a little visit. Sounds like a nice chance for a break for you maybe? I can't see a big problem with that at all. Remember the ex is probably not in a good place right now.

This is sensible. Just have a couple of hours to chill on your own while they are out.👍

This goes both ways though doesn’t it. If your happy with the ex being on her own at Christmas then why wouldn’t you want to be on your own?
But you don’t want that because you know it would suck. A compromise where the adults can be civil for a couple of hours for the sake of the kids is the least objectionable in my opinion.

I'd go for inviting them all for Christmas lunch, especially as my own family would be there too. She'll probably decline anyway, but you've shown willing. And if she does come, it will be time-limited and doesn't need to be awkward - could be quite the party atmosphere. If she causes an atmosphere it will be her who loks bad.

She doesn’t want to.