Why would any parent do this???????

I have this friend who recently moved back in with her parents and her younger brother. The other day she was on the phone with her boyfriend when her brother told her he wanted to use the phone and she said no.. The phone got hung up and a little while later I got a phone call from her saying that her brother attacked her and she couldn't see out of her eye because it was swollen and blury. Then the phone got disconnected again.. After a while she tried to get the phone again and call to let me know how she was doing and when she grabbed the phone her father grabbed her by the throat... What kind of brother would do that to his sister and what kind of father would do that to his daughter.. Then on top of all of that her mother would do anything to stop it.. The only thing her mother said was you don't know how she treats us.... I Don't Care.... C'mon... I have two daughter and if their father ever did that to her he would be dead.... I wouldn't care how she talked to me, she would be getting treated like that at all.... If I had a son and he did that to his sister he would get put back in his place or he would be goin to jail to learn a lesson.... I know that brothers and sisters fight... I have a brother but I know that no matter how bad we fight he would not intentionally hurt me like that..... My friend is now staying at a hotel and she has to find a way to another hospital to have her eye checked because the hospital that she went to told her that there was something in the back of her eye that was messed up and they didn't have a specialist there that could examine it.... I really hope that she gets the help that she needs... At least for now she is out of that house and not being put in danger and nither is her son...... If you have anything to say about this please do.... I would love to hear your input on this situation or on any of my writings......