Hi Audrey.
The dynamic here sounds like a very difficult and sick situation.
The only one you can control is you. You can not effect a change in the behavior of others.
If it were me, I would either not go, or limit my time there to a couple of hours, or just for dinner.
The issues you are describing , IMO go way beyond spending Christmas time with the family. Your unhappiness in this situation sounds very deep , for good reason.
This dynamic is not going to change unless there is a willingness by all the players.
It sounds like a grin and bare it situation , or a situation to avoid altogether.
Take care of you. Katie