OK, here is what I am suggesting to try. Each rooster has his own cage but place them close enough to see eachother but not close enough to get "riled up over it". Slowly [over the course of days] move the cages closer together, if there is squabbling do this:
Since they all know you well, you can start instituting a new rule on them...YOU are the top rooster. Teach them the word NO followed by a tap to the back of the head/neck [just like they do to eachother] everytime they start to give eachother the "eye". When you have noticed they back away from the NO/ thump you can try doing just NO raise your finger at them and stare them down....When this works, then you can try supervized outings together for short periods of time so you can interviene if a squabble starts.... I can't tell you how long this will take but it will work if you give it enough time. I have 4 serama roosters that live together in a run/coop and I used this method and now everyone gets along OK, yes there are occasional spats, but I just use the "I am the boss" rule and they back down......
This WILL NOT work on game stags ever because fight to the death has been so ingrained in their minds thru selective breeding. [just saying].....
Does not work on my game stags or on American Dominique. Latter are not game. They have actually scrap to work rank. Additionally OP's birds are all cocks based on age so stakes for them are higher than stags.
