So as usual, the kids have plenty of alone time with their dad, and it doesn't seem as though op is trying to push herself into the relationship. They’ve had five weeks and scattered weekends throughout the year in which they’ve spent time alone with their dad and been catered to with regards to food, and probably activities etc, as it doesn’t seem as though op and her dd have been included all that much.
And with this visit, they’re again staying for a week so seven days in total. One or two of those days (I’ve lost track- sorry!) will be spent carrying out traditions specifically for them - which they will have already experienced at their mothers the week previously. So it seems as though they will probably be catered to for more than half the week - their second christmas, plus other days out and activities alone with their dad on most other days, I bet.
On one other day they are expected to participate in a celebration that is important to other family members (op and her dd) and a couple of other people, which their dad has celebrated before and planned to celebrate again with or without them. There will be food they can eat, even if they aren’t keen on all the options, and I’m sure op mentioned presents that day too? So over half the people there were always going to be celebrating and due to a change of plans at fairly short notice the SC are now being included too. It’s one day - and I’m sure for part of it they can go off and play with their new toys. I doubt op isn’t expecting them to spend all day with her, playing with her dd and entertaining her family- she simply wants them (for once) to fit in with pre-existing plans and eat a meal she has prepared - including British food - without any massive fuss, on a day that has religious and cultural importance to her. If I’m remembering the ages right (which tbh I’m probably not!) the oldest two are old enough to participate in a meal without having a tantrum about it and the youngest probably won’t even fully understand the meaning behind it, and will be happy as long as they get their second christmas.
And I agree, a visit from santa not on christmas eve seems ridiculous. And it makes complete sense to have the cousin's family in the room with a double bed. So what if SS sleeping arrangements change for a couple of nights - he's not the only one who will have different arrangements! It isn't as if he is being singled out, as everyone will be affected and maybe your DP could try and spin it as a christmas adventure? I hope that when they arrive, he sits them down and warns them again he won't tolerate any misbehaving - at least on monday! It wouldn't be fair for you or your family members to have a special day ruined, after rearranging and reorganising your plans to suit your SC and make them happy, because of their mother's wishes.
Also, I hope I'm not the only one getting really curious about which asian country this is - I know google will probably have the answer but that's just a bit weird isn't it? Though I have to say I probably wouldn't enjoy it all that much myself if there's lots of fish, as I'm not really a fan of seafood
Hope you have a great new year, and things go as smoothly as possible. I'm hoping you'll return on Tuesday and say it all went brilliantly without any issues whatsover - I'll keep my fingers crossed for you!