My sister's boyfriend drinks and parties. He also drives drunk and has gotten a DUI. On top of that, he has physically abused her. But he is a good father, so the courts gave both him and my sister the same amount of visitation. But of course, since the girls live with their paternal aunt, he's secretly getting more time with the girls.

I'm sorry your sister's situation is so messed up. My sister's is too. Sadly, I don't think there's anything the court will do if he says he wants equal custody.