I agree with OptimistS. I believe that disfunction is the common factor in cases such as this, regardless of whether someone is married or whatever.
My views on this might be controversial but here goes. I believe in forced sterilisation as an available punishment for cases such as this which are extreme, against children and where guilt is absolute. The God given right to have children should be taken away.
It might be easy to blame social workers, doctors etc etc and I am not saying they are not responsible in different ways (in my opinion people should lose their jobs over this). However, the ultimate responsibility lies with the mother. She allowed this to happen to her child and she is responsible for allowing these men access to her child.
It was her job as a mother to ensure that any man she chose to live with, respected and loved her child/children and she failed miserably to do that. In fact, she encouraged it simply by allowing the abuse and not only that, but to actually bring another child into the relationship. It makes me sick as it does everyone on this forum.
To put it mildly, the guy was always gonna be a Nazi worshipping scumbag but no-one forced her to sleep with him or live with him. People only do what you allow them to do and she allowed him and the other guy to do these horrendous things over and over. The punishment should be extreme for all of them, and, if there is a worst one out of these three people - in my opinion it is the mother for not protecting her child.
My heart goes out to the remaining siblings who have to live with this trauma.