You say a very big fat NO.
No. I am not going anywhere on Christmas Day.
Honestly - short term pain, long term gain. Save yourself YEARS of shit and put your foot down, and MIL will sulk but she’ll learn that when you say no, you mean no, and when it comes to what you now do as your nuclear family is NOT up to her and she knows her opinion won’t be a priority.
Next year, she won’t even try, and you’ll have set out your stall.
There will never be a better time as you have the whip hand - you have the baby. This is what new parents DO - they start to make their own decisions as a new little family of their own. Don’t let her swoop in and wreck that before you’ve even started.
And you say all this to your partner too. Does he want lovely happy family Christmases? Then he backs you, his partner, with what you want to do together. Does he want you to start feeling antagonistic towards his parents trying to take over, and cause strife between you? Then he runs to mummy and agrees with her. Will he have to do more this Christmas WHEN you host? Yes. He’s a parent now hosting in his own home - um, isn’t that how it should be, or was he intending to play man-child for the rest of his life with either mummy or wifey doing it all? Tell him straight - my parents were happy to respect our wishes and come here. Your mother tried immediately to bulldoze. And that’s why, if you’re not keen on hosting as a father and would rather be a child, I’ll be going with my baby to see my parents on Christmas Day.