My friends parents are Horrible?

Call the police. Then have the girls go to the hospital. Let them examine the girls for not only the physical abuse but the sexual abuse as well. This situation can damage not only you but your friend. I know it may seem scary or confusing but you need to do something. There are also helpful websites or helplines such as 1-800-4-a-child, or 1-800-422-4453. You must do something. You know the facts. Help them as much as you can.