I hope you find your peace, Checkedcloth .
Do you mind if I add something else?
I am guessing that perhaps it is too late for full on revolution this year. But you can start taking steps. Certainly, there's no reason why Boxing Day can't be the buffet affair that others have suggested. Your DH is perfectly capable of opening packets, making sandwiches, heating up sausage rolls or whatever. You can be taking a bath and getting yourself ready, you'll have done the hard yards on Christmas Day, this is your day off before work on 27th. What is your ideal Boxing Day? Games, movie, a walk? Try to get some of that achieved. Get your kids onside. Make it clear to DH that you won't put up with any laziness, moaning or negativity.
As for Christmas Day, try to think of some strategies to make you feel less shit. For example, if your mother complains about the food, have a breezy and witty response ready. Deadpan wit usually confuses the humourless self absorbed types. Either that or a complete non sequitur; she criticises your food, ask her if she likes the tree/your top/badgers.
Make sure that before anyone eats, there is a toast to the chef in acknowledgment of your efforts. Could one of your kids do this? Or do it yourself, bit of chutzpah, make them acknowledge you.
Tell you DH now that you want a beautiful bound notebook for your birthday (make sure he bloody well acknowledges it). Use it over the next year to write a description of a wonderful Christmas that's achievable for you (which will not include a personality transplant for your parents, because that is not happening). Perhaps there's a new ritual you would like to do on the day, e.g., lovely walk, going to say happy Christmas to the ducks or something! Make a list of things you would like to receive and present it to your DH in November with no ifs or buts. Try to get him into doing some meal prep over the next year - try to do it together, make it fun, get the kids involved to do some chopping and stirring. Can you imagine you all cooking Christmas dinner as a family, carols on, everyone having a laugh? Get practising.
You are going to have to force the agenda you want, they are not going to change without you kicking them up the arse. But if it gets you nearer to a magical Christmas 2020 and beyond, it will be worth it, and your own kids will have a lovely legacy passed down from their mum and dad, which has got to be the best gift ever.