Go to his house for Xmas. Be fun, be lively, be "you". This is for your girls and not him. They are excited about you being with them. This is new to them. Treat him as you would a casual friend. Don't let it go further than that, no matter what.
You need to distance yourself from him, but not your girls. You are doing this to yourself!!!! He's trying to make a "friendly" R work for the kids. This is to your advantage. Think of it in this way only and don't let him get to you, no matter what.
Jo, I know this is difficult for you, but he really seems to be trying to let you be a part of their life lately. He doesn't have to be your H for this to work. Lots of us have to do it this way also. You're fighting it. In your eyes, it's all or nothing. This is ridiculous. Be their mother, with no connection to Andy other than he being the sperm donor. It's the way most divorced people work it out, unfortunately.