Have any of them been fixed? If not, I would say have them ALL fixed and the fighting will stop. Chances are the fighting is hormonal--survival of the fittest. The strongest male "wins" the female and the right to breed and carry on the genes. Once they are neutered, they lose the instinct to breed and the fighting stops. But you need to have her spayed as well.
My best advice otherwise is to not break up the fighting. The fight is a dominance issue. One will eventually win, the other learning to back down, and the fighting will stop.
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