I am so upset, FIL has refused to go with our xmas plans this year and now I don't know what to do.

Leave him to it then. Why should you be forced to spend it apart to please him ? Sod that, he fits in with your plans or not as he sees fit.
presumably he has spent many days alone since your mil died and quite capable of being alone.
no doubt he is just trying to gain the upper hand and thinks you will capitulate, I'd just leave him to it. I'd bet £50 he will change his mind if he sees you won't cave.

You aren't being controlling at all, you are mistakenly thinking (you may have been conditioned to think this) that it's your role/job to make people happy. It's not, you can't make people happy that's all on them. I expect on Christmas day you will feel awful inside as if you've done something terrible not being with him but to use corny therapist speak you'll have to just sit with the feeling and it will go away. You probably have that feeling now and you are trying to do something to stop the feeling!

This. Sorry but he cannot dictate what everyone else is doing. He won't thank you for it. Be firm, it sounds lovely

Do you know that FIL is refusing to come because he wants things as they were? Or have you just guessed this? Maybe he's an old man who tires easily and often doesn't feel great and thinks that a lazy Christmas Day to himself maybe with a light tea and an Xmas movie with his grandkids in the evening, would be great!

Just leave FIL to do whatever he wants to do and if that means being on his own then so be it. He's a grown-up. He's been invited so he can't feel left out. Does he live close enough for DH to take him a dinner? If so, he's got the invitation to come round for the evening if he wants to.

he has said no. He doesn't want to go to theirs. This throws our plans completely out of the window, we can not leave him to spend Christmas day alone

I never understand why people decide whether others can or cannot spend xmas day alone.

I am glad from your later posts that you are now allowing him 🙄the autonomy to be on his own. I will be on my own, by total choice. I would NOT appreciate others deciding otherwise for me.

I'm in my 70s and in my time have spent several very happy Christmas Days on my own, but oh the pressure! I would dread telling people I would be on my own, they'd pile in with all these offers and suggestions and it was such a flipping effort to convince people I would be much happier on my own.

Let him be on his own. You have given him a choice, he has chosen not to come. He knows that is he refuses he will be on his own.

I think you might be right @Dreamsfallapartattheseams, if he's a rigid personality, he may feel uncomfortable in a new environment and he may also be afraid of your Mum's illness. I think it's best that you take him at his word and pop his lunch down to him.

You're trying to make everyone happy and sometimes that's impossible! You're doing your absolute best, and you sound like a lovely person.

this!

That said, it's no tragedy if FIL is alone for the day.

Of course not, especially if that is what he has said.

I can imagine my Dad saying it but not really meaning it🙄

He was often wanting to do what was easiest for the other person, but sometimes you want the truth or a decision!

"Tea or coffee Dad?"

"Whatever you're making/is easiest"😂

Can't FIL come to you in the evening to watch the film as well?

Do this. Your DH can go see him in the morning and bring him some nice food, spend an hour or so with him, have a pre lunch drink with him, and then leave him to his early lunch, go to you mum's and get on with the rest of the day according to your plans.

I know. Many solo people would be thrilled to have had with 25/26 Christmases with a beloved partner. Read the room.

That said, it's no tragedy if FIL is alone for the day.

we can not leave him to spend Christmas day alone which means dh will now have to spend lunch with his dad and my dc and I will have to go to my parents as planned (dc find FIL boring so won't want to go to his). This will be the first time in 25 years that dh and I will have Christmas apart.

I mean honestly if your husband does spend some time with his Dad would it be so awful?

I agree with that if he's been invited and has declined then you just leave it there. But I don't think the fact that his wife died in 2020 means that he should just do whatever is daughter in law wants. My husband died in 2019, and I still don't really get the same pleasure out of Christmas. I certainly get little pleasure spending it with family. Chrismas is as much about memories and tradions, and so if you are not careful its a day long reminder of what you don't have. So I spend it with friends. But, I have also spent a couple alone, and it's been bliss!!

Honestly as an older person I wouldn't mind being on my own at all. If he's quiet he might prefer to stay on his own .
You say he likes to eat early.
I would drop him off a plated lunch on the way to your Mum's house and have a cup of tea with him. Perhaps give him a few edible treats for while he's watching TV. If he has time your husband could pop over for an hour later.
If your FIL really doesn't want to be alone he will "change his mind" when he hears the definite plan.
As long as he has a clear mind it's fine to tell him what the plan is and let him make his own decision. No need to treat him like a child.
There's an open invite to come with you to your Mum's or you will bring his lunch over, which is kind of you.

I think I’d gently explain to him that because of your mums dementia this is going to be the best way for the foreseeable. Tell him you really want him with you and will be sad not to see him for lunch, and also that you are exhausted and would like a quiet evening in your own home. He might be thinking it’s just a one off, but it sounds like this might become the pattern until your mum is no longer at home. I’d let that sink in for him and see if he comes round a bit.

I really feel for you. We had our first “us” Christmas planned this year but then FIL died suddenly so now we’re back to the usual plans of not spending it in our own home. One day…

I think you, DH and kids should go to your parents. I can think of a few solutions that may help regarding FIL:

1. My local pub is hosting Christmas dinner for people on their own, I'd get details if there is something similar near him and ask FIL if he wants to do that.
2. Offer him an M&S Christmas dinner ready meal for one that he can pop in his oven and leave him to have a quiet day if he is a quiet man.
3. If he doesn't want to do either of those, offer once more about your parents and if he declines, so be it, it's ultimately his choice.

Sounds like a compromise is emerging. Also your FIL could spend boxing day at yours instead. Its not going to be much fun your dh and him alone on Christmas day.

It feels like everyone is pandering to one lonely cantankerous old man, whose own daughter no longer speaks to him, and expecting the women to just rally around him in spite of their own challenges. OP's poor mother has alzheimer and OP is her carer 5 days a week

We really do expect very little of men.

I would suggest DH goes and sees him for lunch then comes back for your evening together with DD.

You are dealing with SO much OP. You cannot accommodate everyone. You are right to prioritise your mum and I think in this case your DH should prioritise his dad. If anything it will show FIL that you cannot always work around his plans.

I think the change of location for Christmas lunch is a slight red herring. The other (major) point is that you no longer want FIL over in the evening, so it seemed to make sense to essentially get everything out of the way early, to free up your evening with DD and DH. Of course that’s hurtful to FIL.

Not saying that you can’t do what suits you, but I suspect FIL’s refusal is about more than just not wanting lunch at a different location.

Does your FIL actually want someone to take a Christmas Dinner round to him? Has anyone asked him? He might be perfectly happy to just cook himself cheese on toast, or whatever he likes.

Going to yours for a big Christmas meal isn't an option and of the choice between going to your in-laws or not he wants to stay alone. Could you or DH ask him if he'd like someone to pop in earlier, or later, or is he genuinely happy to be alone?