Should I go in as a third party and fight for custody of cousin’s children?

A lot of factors between both divorced parents can be considered like domestic violence, marijuana use, prescription drug abuse, and alcohol use. Father has a record. Mother’s boyfriend has a twelve criminal charge history who is in prison now for dealing drugs. She's been in a lot of domestic violence relationships. She now lives with a man who snakes crack. She's an alcoholic. The father smokes marijuana with his new wife and goes out drinking leaving the children home to watch the baby ages 12 and 14. He has caused a lot of domestic issues on the mother. I've always tried to help improve her. It’s become pointless to help either. I want to help these children and if need be take custody. In the past through the court, I've always expressed best interests of the children.