When you were a kid did you have siblings? Inevitably you probably fought with them. Maybe you both fought for your parent’s attention. Or possibly one of you was bigger and beat up on the littler one.
In both humans and dogs this is caused sibling rivalry. Sibling rivalry occurs when two dogs living in the same household fight repeatedly and aggressively. It may start with snarls or growls, but can then progress to vicious, prolonged fights. We are not talking here about short arguments. Sibling rivalry that is disruptive to your household or to the lives of your dogs is when the problem needs to be addressed.