I have not gone through that specific kind of situation, but I want to ask: do you have a good lawyer to rely on? I would obtain legal advice on how to get the majority of custody, if not full custody. Your children's father is doing far more damage than good. He is not a good role model or parent whatsoever. And the kids will suffer under his hand if it's 50/50 custody. See what you can legally do and obtain legal counsel, is my advice!