Cut your loses and run. The more you attempt to regain what you have lost, the more 'in control' he feels. Give the cad absolutely no power in your lives. Deal with him only through officials and whatever you do, do not let him know where you are.
Most importantly, get mom into counselling. The worst part of a situation like this is that it damages your trust in others. It will take awhile before mom feels safe enough to trust anyone.