I don't know anything about your sister's ex-husband, but I am familiar with many cases of domestic violence. I do know that protection orders from a judge, barring a determined and violent ex spouse from the premises, are meaningless. Hopefully, your sister's ex will move on.
Perhaps, but out here if the little woman calls the police and shows them a protection order it is more likely that hubby gets arrested. The problem with getting one is just the fact that you seek an order can push someone over the edge. This is getting away from the OP's issue.