Are there any psychological issues going on when brothers fight all of the time?

Depends. In the younger children, it is a form of play; rough-housing. It should never become serious or be met with parental approval. Also, it is never funny. To learn and develop is good. Parents should try to channel behavior appropriately. Bothers should also be kind to each other. If 1 brother dominates the negative sphere, counseling my by necessary.
Usually Not Serious. In kids, there usually is a certain amount of sibling rivalry and competitiveness.I allow no slack for physical altercations, holding both kids responsible for avoiding dangerous fighting. Everyone suffers thge "punishment" for fighting. For verbal scuffling, i chase them to another room to settle it. And lots of discussion explaining potential harm helps.