As this keep popping up, I have more thoughts.
I think you have to figure out what is most important to you. Drawing a very hard line--we are doing X at Y time. If you want to see us, you will do so at that time." EOD
If only have one activity is the top priority, that's what will get it for you.
But you can also ask yourself if there's room for nuance. Maybe you just don't want to work so hard, in which case perhaps you can consider alternatives, like a calm date before or after the week of Christmas, on which you cook a couple frozen pizzas and chill, watching a Netflix movie with your mom and your kid. Or bagels and cream cheese with your dad and stepmom before they go off to celebrate with her family. Or whatever.
You can flex and remove some of the things you complained about, but probably not all. Of course you don't have to do so. Whether or not it is the right answer depends on your priorities, and how strong those priorities are.
So, what is most important? Consolidating into one day? And then what's second most important? Because you can do #1 on Christmas day, and you might see dad and step mom for a brief time, and maybe not mom at all because she knows dad is coming. But if doing it on the holiday is the second priority, that's the right answer. If, on the other hand, the second priority is maximizing the chances of seeing everyone, then maybe you pick a different day, but still do one day. But maybe #1 isn't actually "one day", it's "less stress", in which case that pizza with mom on January 11 might be the better choice.