We weren't groomed to look out for each other. Yet we're still best friends. Everything went wrong that coule. My mom's parenting style is destructive and my dad is passive. If he would have jumped in and fostered the kind of environment that he had, we would have been great off bat and a lot could have been avoided. However, he was providing most times and not nurturing full time, which makes sense.
Anyway, until I was about 18, we multiple bouts of estrangement and hostility between us. I noticed that my mom and he r siblings were worse than is, and that she was making it worse b/c she thought it was normal to hate your siblings. She'd gossip between us, lie, instigate, tell us that we were jealous of her favorite, who's life was in shambles at that time, etc, etc.
I learned at 12 that something was wrong with my mom, and since then I've realized that she did not know what was best for our family. I made the decision to work on our relationship. I had a model in my dad and his sibs, but I just went off instinct. My little sis and I were already close, but the relationship was still forged from anger at others around us. I told her that I don't want that for us, and that I don't want us to be like my mom and her sibs.
Her and I started to work on our relationship when I was a young adult. Basic relationship guidelines, honesty, respect, communication, love and affection. Eventually, the others fell in line once they noticed how strong our connection had become.
One day, I was speaking to her quietly over my parents house, after she moved back home. She called after I left and said that my mom had been eavesdropping and told her that she wishes that she could be like that with her sibs. I said that she possibly could if they all weren't two faced and evil.
They're always trying to one up each other, and they gossip like monkeys. So yes, I think that jealousy plays a huge part of it. Not knowing to handle jealousy will obviously cripple any relationship in your life.