For some context, my older sister is developmentally delayed and pretty much has the mental capacity of a preteen. As far as I'm concerned she pretty much has no agency. Her husband is a psycho and has basically been holding her and the kids hostage for years. She has no phone, no computer, no car or license, and cannot leave his sight. I have no idea if he's physically abusive towards them but he does have a history of explosive anger and violent behavior towards others. When he was in school he pushed a kid down the stairs and was expelled, and more recently he pulled a gun on a family in a road rage incident but miraculously had it expunged from his record and didn't go to jail.

We haven't see them for about 3 years and the last time my mom tried to visit, the husband filed for a restraining order. They live in a trailer with no AC or heat, and they all sleep on the floor. They are homeschooled and have absolutely no contact with the outside world and no social skills to speak of. The last time I saw the oldest child she was basically unable to even speak even though she was about 5 years old. I think it's too late for her at this point rendering her basically a feral child. I really don't want that to happen to the two younger ones as well but we're running out of time as they grow up and miss certain milestones. CPS has been called multiple times but they never do anything besides requiring the parents to buy certain items for the kids. He would buy what he had to and then after CPS returned to check up on them would just return the items or throw them away. Any ideas?