What a painful and frightening situation to be in. Everyone else gave such good advice.
Do the right thing. Keep doing the next right thing. Deciding what the right thing is can be so confusing sometimes. Keep in mind that you are NOT all this man has. There are a batallion of professionals out there at his disposal and they can really and truely help him, but he has to decide he wants that. If those kids are put in foster care it is NOT your fault. It is because of the actions of those that are responsible for them (and that is not you).
Your only responsibility is to do the right thing, and then the next right thing. You do not have the power or the responsibility to control the outcome. Just do the right thing and let the outcomes happen. I know that is very very hard to do but you are a smart, strong and caring person. Reach out for support of your own. Focus on you and finding the right thing for you - and the kids. Do not focus on and worry about the other adults. They have to do it for themselves, just as you do. The kids have no voice and no choice. I always advocate taking into consideration the right thing for the kids when making a decision. The current situation can not possibly be in their best interest. You do not have to solve that or worry about the end result - you just have to find what the next right thing is and do that. (I'm not judging - I was clouded and confused on that for a long time with my own children and I'm not young). Hang in there.