oh @birdsintrees you poor thing, I have been in that crisis mode (in my case after escaping an abusive marriage) and your head just shuts down - it's in "fight or flight" mode and doesn't allow you to focus on details because it doesn't think they are important. And at the same time it also gives you random, relatively unimportant stuff to think about as a way of avoiding the real issues you have to deal with.
In your situation I would: park thinking about Christmas until a specified date, say 1st October, especially as you're going to be at home (unless there is a friend/family member who could host you, but only if that wouldn't be any more stressful than being at home). Give the girls a budget and get them to manage the whole thing - they'll almost certainly enjoy it, they can decide the activities, the menu, the decorations, all of it.
Then just roll with it...us mums often have this idea that we need to make everything perfect for everyone, and that's daft...bizarrely, one of my favourite Christmas Day memories as a kid is my boyfriend knocking the tree over trying to catch a guinea pig (the rest of Christmas had been shit, parents in the midst of acrimonious divorce, no presents bought and I had to plan, buy and cook dinner on Christmas Eve) but the moment of my BF sitting underneath the tree, guinea pig in hand, both covered in tinsel and baubles is one I will treasure forever!
Good enough is good enough...do the easy thing...and all those cliches - go with all of them just now, and take care of yourself.