First, have they been fixed? Unneutered males will fight sometimes. Could be stress too. Any major changes in the household?
I would try Rescue Remedy to calm things down. You can get it at health food stores, Whole Foods, and a bunch of other places. A few drops in their water or rubbed on their paws or ears can makle a world of difference.
Try giving each one some personal time alone with you. Cats need 10 minutes a day of personal attention for good emotional health (some need more). That can help too.
I know how it goes sometimes. my youngest picks on my oldest sometimes and can get really rough. I've broken up a number of fights, but Zenobia has gotten the idea (finally) that this behavior is unacceptable and toned things down quite a bit.
Good luck.

Also try Feliway. It comes in a spray that calms them. I don't know if its the change in season or what, but all of mine are CRAVING attention! I am having to make sure that each one get "special" time and play. My youngsters are going crazy chasing the lazer light and this is helping. I also will have only one in the bathroom with me at a time so that there is no sense of having to share. Its keeping me busy! (But I love this kind of busy!)

It seems like the males have an issue with being the alpha male, whether they are neutered or not. Neutering is definitely needed, of course, and it will help majorly. However, my males are neutered and older and they still have issues with who is boss. They know that they are not supposed to fight, but they do have a few personality clashes, still. Thomas (alpha) and Stanley will never get along. Just don't like each other. No major battles, just occasional friction. Both are very large neutered males, and older, (Thomas about 12yrs and Stanley about 18yrs....not young cats) and they have been together for about 7-8 years or longer! Maybe I will get some Rescue Remedy and try it on Thomas (the instigator), he likes his ears rubbed so it would be easy enough (at least the first time).

I have a neutered male who will just not tolerate a female stray I adopted. The stray, KC, is quite happy to live outside of the male's way. This mornin my male found another cat in my laundry (the door was open) - I have never heard the sounds before that came from my cat's mouth. I managed to case the intruder away but my cat continued to scream and growl at me, scary. It took a lot of talking and petting to relax him. But I am going to try the Rescue Remedy, see if that works! Have had a number of cats, both male and female but never this problem. Hubby reckons my male is the alpha cat and comes before even my hubby, maybe he is right!

not sure. Are they fixed? If they are I cant say why. Sorry.

Zenobia is very territorial. She'll yowl at cats that are sitting in the windows of their OWN HOMES. And God help any cat crossing the property. She'll go after raccoons, opossums, skunks, whatever. I'd have some serious problems if it weren't for the fact she gets walked on a LEASH and I can stop her before she gets into too much trouble.