I would not worry about what your other daughter is doing at all. If you block her you will not even be able to see what she is tagged in.
As far as the holidays, I would celebrate them on an alternate day w/your son and his family, and just explain that this means so much to you to spend w/your friends, so you want to do both.
I would never be able to fit in one day all the celebrations we go to around the holidays. I like celebrating on different days, it spreads out the fun!