I need advice! Sorry for the long post, tmi

My stepsons bio mom is bipolar (not saying that to be petty she really is) and won't take meds to help. I just found out through a co worker, who is her next door neighbor, that she leaves my stepson (4) and her 1 year old baby alone in her apartment for hours on end. On top of that her new baby's dad is her half brother. When she's on an up, which she is rn we get along fine, but when she comes back down she screams about me and calls me names in front of my ss, when my husband gets back from his training we are thinking about fighting for custody. This would be his 3rd time filing and we've made a police report about the incest, and she still has temporary full custody while my hubby is gone, I don't know how to protect my ss or how to handle this by myself, please help!