My girlfriend has postpartum psychosis and signed over her rights. I don't want her parents is our lives?

I just turned 19 and my girlfriend (well, kind of ex-girlfriend) is now 17 and we have a 4 month old son. I’ve been with my girl for 4.5 years and I love her more than I can ever describe. Her parents are Satan’s workers and I mean it. These people are f***ing evil. The first 2 years of our relationship, they loved me but when I started encouraging her to go after her dreams and not theirs (she wants to be a lawyer, they want her to go into the family business) they did a 180. They did everything possible to keep us apart, but we were in love. I found out she was pregnant in May of last year. It wasn’t planned but I vowed to be there for her and our child. They waited until the end of the school year, withdrew her from school and sent her out of town. They said that we were NOT keeping the baby but I told them it wasn’t their decision. My parents threatened to get the police involved since we knew she was pregnant and they wouldn’t tell us where she was so when she was 6 months, they literally dropped her off at our house and said “Keep her!” I was happy to see her again but she was different. She seemed depressed but she said that she was sad her family was acting the way they were so I attributed it to that. She had our son in January and that’s when the real nightmare began. She was severely depressed, refused to eat, developed really bad insomnia (I mean she STOPPED sleeping) and she began acting delusional. She seemed maniac. I knew I had to get her to a doctor but 2 weeks after he was born she took off. We searched everywhere and the family swore they didn’t know where she was (that was a lie; they were hiding her from us). When he was 3 months, she showed up at my apartment with documents stating that she was signing over her parental rights. She looked as if she had been living in a sewer. I asked her why she was doing this and she said “because dying is so much easier.” I didn’t let her leave and called 911. She fought hard, but they took her because once I her got inside, she had an episode and began trashing the place. She was hospitalized for 3 days. I told the doctors I thought it was postpartum psychosis because I had been looking up her symptoms online and they matched to a T and they confirmed it. It was so depressing to see my son’s mother in that state. They heavily medicated her and while she was under I asked her why she didn’t want him anymore and she said she did but that her parents made her give him to me. I called them and said soooo many things. I told them if they EVER came near her, I was going to be their worst nightmare. Her mom just laughed and hung up. B****. I promised to stick by her no matter what. Right now she’s on antipsychotics, antidepressants, and antianxiety drugs and she goes to a support group at the hospital. She’s doing so much better. I don’t leave her alone with him because it’s only been a month, but we’re getting there. She lives with my parents but I see her every day. So that b**** called me today and said that her and that fat piece of s*** of a husband wants custody of OUR child. I literally want these people to die in a ditch. I KNOW she can’t take our child, but is there any way they can be prosecuted for the things they did to my girl? The way they treated her when they KNEW she was sick was just inhuman and I’m pretty sure illegal.