AITA for removing my son from this situation

This is very complicated so bare. My son is 15 now. Back in September of 2024 when he was 14 he told me he got a girl pregnant. Obviously I was not happy about that. The girl he got pregnant was 13. She just turned 14. I spoke to the mom on how we were going to go about this and I was hoping they would go abortion because they're both so my young. She wanted to keep it. I said my son would step up and we would help anyway we can. Especially since they were in poverty. I bought everything for this baby. I made my son take parenting classes. I tried to support her the best way I could. My son's therapist and his caseworker were trying to help. He has a caseworker for mental health reasons because he struggles with PTSD. I told my son adult actions have adult consequences.

Fast forward to May 9th. This baby is born. They're at the hospital. There was a lot of conflict with her mom about how involved she actually wanted my son. She didn't really want him over the see the baby. She did want child support. Since he's underage I would be the one responsible for child support. May 17th my son shows me some texts between him and his "baby mama". She confessed to him that this baby is not his. She was already pregnant when they had sex. Her dad had been sexually abusing her since she was 9. He is the one who got her pregnant. The mom knew this but didn't want her dad to go jail so she told her daughter to have sex with another kid so they can say he's the father. And the other thing is in the beginning I was suspicious of the timeline between when my son said they had sex and her due date. He said they only had sex once which I assumed he was lying about and just assumed they had sex more than once. I ordered the paternity test the second I could. And yeah he's not the father. The stuff with the dad is being handled by CPS and her and the baby were taken into cps. I eventually explained the situation to my friends some think I should have let my son stay on the birth certificate so that we could take the baby because now it's in foster care. This is gonna sound cold. Not his baby. Not his problem. It's not his job to save their girl and her baby. The villains are the dad and the mom. We just got roped into this. My main focus are my children. I feel awful for her. I feel awful for the baby. It's not my son's baby. He has no obligation and neither do I. And sure maybe that's sounds cruel but again he is 15. He's a kid. Not his job to provide and save a baby that is not his and it's not mine either. He's off that birth certificate and out of that situation and this situation caused him more trauma because that dad was horrible to him for getting his daughter pregnant knowing damn well he didn't. Saying things like he should shoot him for getting his baby girl pregnant. I want nothing to do with that family and we have no obligation to that family

Edit: The parents are both in jail. Dad was child s.a and incest charges. Mom for failure to protect. I think the mom is trying to get out on bail but I don't think I'm getting that baby stuff back or the money. Idec. I just want to never deal with these people in our lives again. The whole situation set my son back like 10 steps in therapy. I don't even care about the baby stuff. I just want these people to stay away from us. I'm just glad we got the paternity test and everything before we paid any child support