K.B.
My niece is on the aggressive side and for a long time I didn't say or do anything because I didn't want to offend my sister. Then one day I realized that if I wasn't going to protect my kids then no one would. Now I firmly lay down the rules when my niece comes to visit and I don't care if my sister hears me being firm or not. Since I have started doing this, she behaves better at my house than she does her own; and my sister has never said anything to me about it. She will even back up sometimes. Good luck.