I have a friend that has several different breeds all male and all different ages (collies, deerhound, brittanys) when the pups got to an age where they start to flex their muscles alot of fights happened as it upsets the balance. But she also had a problem when her eldest dog who would usually sort out the fights and keep the peace got ill and the two younger dogs were fighting all the time, it got worse when her older dog died. I know people don't believe in a pack mentality but sometimes it does make a little sense.
I know Sue sorted out her dogs problems with alot of time patience and training. I can ask if you can pm her if you like?? She's a lovely person and might be able to offer you a little support?