Tough situation.
Your best bet is to file a petition for modification of the custody order that's in place.
To be perfectly candid, the fact that the grandfather is not in the house with the children is a big factor. If he is not present, it will be easier to argue that the father himself is not a threat to the children. You would have to show a correlation between the grandfather's action, and the father's, to make an impact in court.
I recommend contacting your local bar association, or contacting an attorney in your county/area. Best of luck.
Answered on Jun 01st, 2016 at 12:32 PM