This is different than most questions about integration. Good!
I'd wait until about half the pullets are laying. Those roosters may be a year old, but they are inexperienced. I'd not put them with pullets where none were of laying age. They may get over-aggressive.
The mating behavior is not just about mating. It is also about dominance. With that mix before some are laying, the hormones and such might not work out too well. I'm talking about the pullets' hormones too, not just the roosters'.
When you put those roosters with the pullets, they will probably fight. It will totally change their "flock" dynamics. If they have sufficient room, there is a tremendous chance the fighting will be a lot more chasing and running away after a few pretty serious skirmishes. If your space is tight where they cannot run away, it is much more risky. It's possible you won't even notice much fuss between the roosters when you mix them with the females or they might fight to the death. You just don't know. But people do it all the time and it is usually successful if there is enough space for them to work it out. It really helps too that the two roosters are familair with each other.
There would also be some skirmishes if you added another rooster or two without any pullets, but those would be more for pecking order, not flock dominance with females involved. Adding females to the mix really stirs them up.
