Fighting cocks are bred to be aggressive and are goaded in the ring, so I wouldn't worry too horribly about that. I've read that 3 roosters are less likely to fight than 2 (go figure). Also that if the roos are raised together with the pullets, they're less likely to fight--and yours will be arriving at the same time so that's good. We've probably got 10 or 12 roos here and fights very, very rarely happen because we've got docile breeds--Marans, Silkies, Welsummers, etc. And when the roos do disagree, it only lasts seconds because the pecking order here is well established and the lower-ranking roo backs right off. It's usually over hens--no, you can't mate with her!--kind of stuff. One roo squawks, the other one runs off. No biggie.
The last time 2 of our roos fought, it was hilarious because it was the little bitty Silky rooster against No-Face, our beakless Maran roo. One too little to win a fight, and the other without a beak so he can't win fights either, and neither with spurs! They just kept jumping at each other without ever making contact. Silly boys!