Take a breath. Now take another.

You have the support. Going to the wedding will mean a LOT to your daughter I'm sure. Go for her. You don't have to stay for the reception. Stay for as long (or as little) as you like. The focus will be on her, which works out. Hang out with your ex and your little ones, congratulate your daughter, and that's it. That's your whole part in the deal. You can do it.