We have two boys, one is a dobermann mix 14years, other is a komondor 3years old. We had to separate them at 1,5 years of the small, because the dobermann is so dominant and can't understand it would be a bite for the other to kill him... It started as him playing rough, and humping (for dominance) the small all the time, and he didn't care at first but then the komondor lost trust in him. He's very protective of us, and decided the dobermann is a danger, so one day , when he didn't back off from us when warned and started growling, the komondor attacked. We got in the middle and it wasn't fun, even as a puppy he was super strong.
We asked for advice from the vet, but he said castrating the dobermann will not stop this. Then we asked a trainer friend, who said he saw our dobermann is not okay in the head and if he have some brains, he should understand that he's no boss anymore, just let them together in the garden for some hours. Actually never understood and they live separated since, for our own safety, as they started to fight around us because of the other 'protecting'. If we were not there, the komondor took all his stupidity with patience anyway.
The last fight happened when we had visitors and one of them didn't stop the dobermann entering the house even if warned. The komondor charged at him and put him on the ground immediately, stood over him until he got calm, then escorted him out of the house. Imagine me putting everyone in a room until they left and I could call the young back to seperate them again. Unfortunately he still doesn't understand but he's getting paralyzed and have to be put to sleep soon, this is our end of this. I hope yours will turn out different, but maybe the vet would also not help. The dobermann maybe wasn't socialized with his siblings, as he was found on the street very young, 5 weeks, so I think yours should work out the dominance order by themselves but please be careful around them. The trainer said never stop a dog fight, as it will make the other think it won or at least the fight had no consecvences and gave no chance to calm down, causing more frustration the next time.