Living with another family with a child the same age as my own.... problems of opposite parenting

My son is 3 years old, and I am expecting a baby girl in a few months. We live with my husband, my sister and her husband, and their child. My nephew is only 20 days older then my son is, but their personality’s couldn’t be more opposite. My husband and I are very hands on with our son, we discipline him, we reward him, and we try to work with him on learning. Yes, discipline at 3 seems weird but we were both raised in families that didn’t really expect much from us that never cared what we did regardless. Sometimes my husband can be a extremely strict and harsh, but it’s just because our expectations for him are real. Now living with my sister is hard because their parenting is 100% opposite what ours are. They don’t discipline at all, maybe once in a while and generally he runs wild, curses, hits, and bites for no reason. I’m having trouble because he is always bullying my son, who is not a mean kid at all, in fact from living with his cousin he is a bit of a cry baby. I don’t know what to do because I don’t want my child to be weak but when his cousin is constantly attacking him for no reason taking his toys and leaving bite marks that scab over I don’t know how to handle the situation. I try to tell him to fight back, but he doesn’t think he can plus he’s to nice to even try. Help. I’m desperate I feel like I’m being a bad parent because everyone is telling me he is a cry baby. via /r/Parenting https://ift.tt/2JK7IdK