Mopsey, First, I'm glad to see the cell phone turned up. I'm no the least surprised to hear that it as found outside. They are so small and can slip out of a pocket, purse or backpack w/o you even noticing. BTW, be sure to tell the man that it was found and he needs to know so that he can't go around accusing his children of doing things that they didn't.
Second, I hope that your daughter does well tomorrow. I'll be thinking about her and sending good wishes her way.
Now, about the christening next week, I think you handled the conversation very well w/him. I do think he wants to show his family that he's doing a great job staying in touch w/his children and yes, the A-one father. They don't buy intohis stories. They have a very good idea that he's being a jerk. So, I wouldn't worry too much about that A-one impression sticking in their minds at this time.
Now, about the "C". You don't have to given him explanation as to why you are not continuing at this time. However, just because you don't go, doesn't mean he can quit either. I think you are on to something about the united front. Take some time for yourself. If you opt to return to "C", do it on your own for the time being. Your "C" shouldn't be pushing anything at this time. He should be listening and trying to find a solution to the issues of your children.
Mopsey, I understand completely how you feel about being around him. He sure isn't acting like the man you once knew. Hang in there. You are doing well despite it all.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.