Am I missing something? You stated that his license is revoked. How do the kids visit him if he can't drive (legally). That sounds like something that should definately impact visitation schedule. How far apart are you and the ex? One option to look at instead of going back to court is mediation. Less attorney involvement, and they seem to be more willing to listen to the kids wishes. But before you do either, make sure it is what they want. He could not want to go now, but still not want the "official" visitation to change.
You can only control what you can control. Try to not discuss or talk about what goes on with the ex. as much as possible. When they return, find out what you need to know, and then try to be a normal family as much as possible. And when they go back, reinforce that if they fear for their safety it is ok to protect themselves by contacting who ever they can, whether police, you or somebody else in the area that they know and you may trust to help them in your place.
I worry some about therapy. I think it might keep him from being able to let go, move on and get past what might have gone on. I think if you let him air out what went on, and how he feels right away, get it off his chest, and then only if he wants to. I would highly suggest avoiding medication at all cost if possible.
While my father didn't put me in danger, he wasn't present. The relationship with my mother and my step-father is what I grew up to appreciate. I ended up calling my step-father DAD and my father was just my father. Put as much effort into you time with them, and less into their time with him.
The world needs ditch diggers too Danny!!!