I'll admit this one has been worrying me a bit this year too - Christmas is a complicated time at the best of times for us and we're looking at cutting down the amount of stuff we're committed to. Previously we have done the following:

Christmas eve - dinner with XP, his other XGF and our assorted kids.
Christmas morning - quickie for ourselves then over to XP's for DD to open Santa presents before they go to his family for breakfast.
Christmas lunch - pick up DD from X's family gathering to go to IL's
Christmas night - BBQ with friends, usually at our place
Boxing day - lunch with my family.

As you can see, it's just a little bit insane. We'd normally spend a good third of the day in the car or on the phone co-ordinating this - this year we'll have a newborn and have decided that DD is now old enough to decide if she wants to be at our place for Christmas or at her dad's. So we'll most likely have our own little family Christmas at home on christmas eve/morning, then head out to the IL's for lunch before heading back home again. Then my family on Boxing day.

A little concerned because thus far XP has been a bit resistant to the idea of DD deciding against seeing him or his family until after Christmas and DD doesn't want to upset him but has said she really wants to be with us for her little brother's first Christmas. Ah well, still a couple of months to nut it all out...