I'm the oldest sibling in my family and I have two sisters(15 and 13). My parents are going through a nasty divorce, and the middle sibling is horribly mistreating both my mom and dad. I hate to see this happen because I know they have enough stress as it is, but they don't do anything, either because they are too short and un-intimidating, or because they don't want to look bad in front of the other spouse. I can't do anything to stick up for them physically or verbally, as my sister is just too childish to actually have a meaningful conversation, and my parents won't allow a fight between us. Please help