Can I get custody of my Niece?

My niece lives with her mother in Vermont and my brother lives in New Hampshire but they both unfit to care for my niece and I wanted to know if I could get custody of her even though I live in Tennessee? The mother is unfit because she is always pawning my niece off on family members and friends so she can go out or just not take care of her. She thinks her cigarettes r more important then diapers for my niece. My brother already lost 2 children to the state and he is thinking with his bottom half more then he is thinking about what his daughter needs. He can barely take care of himself let alone his child. Please help figure out what I can do.