coming from parents that used us kids as weapon's during their devorce I think keeping this as legal as possible is the best. Trying to prove he is a drinker would be the first thing. get records of the complaints you made about he's prank calling etc...
I am sooo sorry you are having to deal with this. There is nothing worse for a family then this crap! ( sorry)Good luck and hug your kids often and always let them know how much you love them! Mine got lost in all their junk and lost us kids.