My answer: my ex and I have a fairly fluid arrangement, because we can be civil. My husband and his ex have an arrangement written into the separation agreement in teeny detail because she can't be civil. (Though that is improving hugely in recent years. I attribute this to the fact that she now has (thank GOD) a boyfriend...)
Our holiday usually goes like this:
4 days with just my kids; 4 days with all 8 of our blended kids; 4 days with just his, and then, because he takes his lot to visit grandparents, I very often got a few precious, precious days on my own. Now my kids are with me full-time over Christmas, I guess that means those days will be just me and my two youngest. (The oldest will have gone back to her own city by then.)
After all that, what I REALLY want is a week off to myself, but what I really get is to GO BACK TO WORK. Woo[expletive deleted]hoo..
But I do love Christmas. Somehow, I really, really do.