Tell Ur husband how u feel on the situation. I wouldnt want my daughter signing that or acting that way. Put ur foot down, let the family know u will not tollerate this kind of behaviour. So what if they get mad for a while. It sounds like they all try to please ur sister in law by not saying anything and letting his happen. If she is at ur home and u are watching her, u are in control, if she is bad, explain what she is doing is wrong and put here in a time out. If she starts yelling and hitting, maybe putting her in a room with the door shut for a time out is whats needed. i believe this is a despreat cry for help, she wants the attension and knows how to get it.