Why do some family's want to ruin or hurt peoples lives?

Ok, i don't know if it's jealousy or i don't know what it is. Why do familys want to ruin other familys lives? It's like if you're going through a tough time they rub there success in you're face but then again. Parts of there success is crumbling down. Living a sh***er life than you're own. But still trying to fix some things in life. Then they try to ruin another person's life and they still want to be a family with a two faced person. I don't get it. Why would family want to stick together after they hurt or lie to them. What are familys for?