What are the rights for children who live in a home where domestic violence is witnessed?

Sadly, DCFS does not have the resources to help children who are not being physically hurt, but are in the presence of violence. Does your mother live with your father? Are you living with them? Are you in physical danger? If so, you can call the police. You can report the situation to the police, and let them contact DCFS about the violence in the presence of the child. It will not help your relationship with your parents, but if you're concerned about getting custody of your sister, it doesn't seem to worry you about getting along with your parents.

It's sad when a sibling realizes the problem more than the parents do. Contact Legal Aid in your area. See what they can do to help you. And don't be afraid to get local law enforcement involved with there is domestic violence in the home. One of the parents can go to jail, and for a short time, there can be some peace and quiet for your sibling.