Child Custody please read just wanted some feed back?

So, I'm the stepmother of a almost 4 year old boy been there since the child was 5mths old. I'm married to his father for 3 years we have a daughter together and I have twin boys that my husband is adopting in 1 week. We are a very close family and wants whats best for his son. His mother is 21 now. She drank and did drugs when she was pregnant and supposedly stopped when she found out she was pregnant with their child. My husband waited for a dna test but it took her 5 mths after the child was born to do it. Came he was indeed the father. But with my husband wasn't there when she had the child to prove she was on drugs so no testing was done. The past 3 1/2 years things have gotten out of control. She the mother was dating a guy who killed his friend but only served 5 years because he was charged as a minor and got manslaughter he went back in for robbing a store and they broke up but she wrote him. During this time she was living with her father and partying when we had him which is every other weekend and couple weeks at a time. Then she let 2 underage kids take her car and crashed it had a lawsuit over her head but it got thrown out because she said they stole her car. Finally, she got own place then about 2 mths ago her friends robbed her apartment while she was out of state still friends with them. Now her sister who babysits just got arrested for posses ion of heroin (she babysits and is around the child ALL the time). When we get the child hes always dirty and wearing GIRL clothes. When the dna was done years back the state sat down my husband and her to discuss child support and medical SUPPORT. Well, she told the state she didn't want support(cause he said he'd take her to court for joint custody and she wants to have control of the child) so my husband pays medical support and they have an agreement through the courts that he wont have to pay if she doesn't get on assurance, so she has full custody and he has shared parenting NOT rights. During these years she's managed to hang onto a part-time job that shes been at for 8 years prepping food. Now with this information what would you do if you were a mother and couldn't do anything about this child..I;ve sat by and been worried about him being with her. She has horrible judgment in my eyes. I'm getting ready to be a college graduate my husband and i own our beautiful home, he's worked at the same very good paying job for 9 years (concrete finisher).. he thinks that he wont get crap if we took her to court because she has always had a roof over his head, clothes and food that we buy. Right now i dont know what to do or think .