If it's your dad's house, he can let anybody in that he wants to, and sell/give away anything he wants to. The kid hasn't committed any crime, so there's nothing to call the police about.
It doesn't sound like a safe situation, though, for you and your mom. If I were you, I'd leave, and try to get mom to come with. If she won't, though, not much you can do about that, either. She's an adult.