You're roosters are still very young, but they will become aggressive maters later on. Over the past 50 years, I've had all of your chicken breeds at one time or another, and based on my experience with them, the RIR roo will likely be the hardest of them all on your hens. Of course that's not a problem if he's the only rooster and spreads out his mating over 10 or more hens. Also, if you thin to one rooster, you will have a lot less crowing because he won't be competing with the other roosters.