Should I do anything?

My mom just found out from my brother that his ex girlfriend is pregnant. She says it's his even though she's been sleeping around with other guys (thats why they broke up) well my brother for some reason wants to help her out...whatever thats up to them. The reason I'm mad is that they both do meth and drink. This girl also refuses to have a check up from a doctor. This is totally child abuse in my opinion. Is there anything I can do?