There are a lot of things that could cause conflict among a family. Some like jealousy, infidelity, and the way you were raised. Jealousy is the natural counterpart of love; when you commit your love to one person, you want an exclusive commitment in return. Anything that threatens that commitment, whether it is another person, a hobby, a job or a situation, causes jealousy. You want the attention of the person you love; when it is taken by another person, activity or thing, you are jealous for the one you love, and jealous of whatever is claiming that person's attention. It can cause the family to fight often which causes family to drift apart which causes emotional problems between the parents and children.
Infidelity affects everyone in a family not just the parents. The children take a large blow from it too. It can cause them to act out. Experts say children who learn about parental infidelity react similarly to children whose parents divorce, except the emotional responses to cheating are deeper and can have greater, longer-lasting impacts. Children who see a parent cheat lose trust in them because the parent was always telling them to be good. But in the end they were the ones misbehaving.
The difference in between parents being raised can have a large impact on the family and how they raise their own children. If a parent was raised in a strict family they might want to pass that to their teaching styles of their own children. But if theres a strict parent and a free willing parent, they may not see eye to eye. That in turn would cause them to fight about how their children should be raised. Which could end up in a crazy custody battle.