Custody of niece

My sister lives In a terrible situation, abusive husband, no access to even 5 dollars. She is disabled, physically, and now mentally as well. The oldest adult son is declared disabled and does not work or go to school. The young girl has been pulled out of school, because of bullying, but no one at home can home school at this point. I live out of state. What steps can I take? Where should I turn first?

If you know (or suspect) people are being abused, mistreated, neglected contact the local police agency. The police will investigate and rescue those in peril.