custody battle

My DH is trying to get full custody, the mother of his child is really young and doesn't take care of his son at all! They live in a one bedroom apt with 5 other kids and 3 adults. And I'm worried for the safety of his son, he's less than a year old and isn't meeting most of his milestones for who knows what reasons. He doesn't have his own room, and he sleeps in a playpen in the living room. Recently the "baby mother" posted practically nude photos on Facebook and I was wondering can this be used in court? She neglects her child, when she's off to school her mother is asleep when he's under her care. She doesn't allow us to have him because of me? but I buy their son clothes, bottles, diapers formula. She gets CS as well.