@Zygon I feel for you and I am horrified about some of the judgemental comments on here directed in your direction. I understand exactly where you are coming from. I've been there ( only it was with my Mum, who passed this summer aged 93) and it's really hard and impossible not to feel resentful about other family members who professed to 'care' very much about her but weren't prepared to give up even ONE Christmas Day of being completely free to do their own thing. They did spend some time with her around that time - but never Christmas Day itself ( apart from 2 years when everyone went to a hotel for a few nights, because it suited them).
Last Year, like you, I was stressed beyond all belief by many things: My children are long grown up, so we took my Mum out on Christmas Day: She had a lovely time and was happy - although my OH and I were not impressed with the meal, or the surroundings and it was pretty grim as far as we were concerned - but what I didn't tell her was that we had actually decided to have our own 'Christmas Day' on Boxing Day including opening our presents, having a bucks fizz for breakfast etc. I couldn't have coped if we had tried to do both on the same day, but she never knew and I was able to cope because I still had the next day to look forward to. So glad we did that as it was her last Christmas as it turned out
Now you have children, so that won't work for you, but as one or two others have suggested, could you take her over a cooked Dinner on Christmas Eve? Or see her on boxing day with lots of leftovers to reheat? Are you sure she has lots of visitors on Christmas Day? She is going to miss seeing you for one?
My experience is that you won't change the mindset of the other family members if you put your foot down and say you aren't doing it/taking the food plate over. I remember many years ago asking if one of my Sisters would take Mum for Christmas Day and being told 'I'm not having her spoiling my Christmas Day'. Yes my Mum was a difficult lady, but the difference was that I simply could not and would not leave my Mother on her own on Christmas Day - I couldn't see anyone on their own on Christmas Day: Others are much more selfish.
So my advice is, do some kind of compromise this year - and next year tell everyone in January or February that you will NOT be providing the Dinner/taking it over to your Gran or both. Make sure they understand that you are serious and make sure your Gran knows that you won't be doing it next year. That gives people plenty of time to think about it. We did that one year, not so long ago. I just said we wanted to spend a Christmas on our own 'next year' and we would be going away so folk would have to consider arrangements. Maybe just tell your parents that for next year?