Do you feel like your are stuck in the middle of all this, as if keeping so many plates spinning? Does your sons wife not get on with your daughter? I can sort of understand your dilemma - however I'm sure it could all be sorted with light hearted straight talking...
Keep calm and put the kettle on when she turns up!
As for Christmas dinner, it seems some folks do get their knickers in a twist. People feel they have to invite other family, and it all gets abit stressy and duty bound.
My sisters daughter spends Christmas Day with her ma and pa, her partner spends Christmas Day with his ma and stepdad.
They have a small daughter, who last year spent Christmas with dad, her grandma, and step grandpa. They toss a coin to see who gets to take the toddler where. Last year mum lost the toss. It all works fine in our family, nobody falls out, and everyone can be totally honest where they want or don't want to be.