I think it's most likely your 3 cockerels/rooster could work out, but it will take more than a few weeks for that to happen. Roosters will fight to establish the pecking order. If you want to avoid injuries, you can introduce them slowly.
Also, from what I hear, Rusty is not particular problematic. When I add new birds to my existing flock, the new birds almost always be lower on the hierarchy as the existing ones consider the land their territory. Chicks and pullets usually accept this, and roosters will often challenge it.
Having a rooster flock has its own advantages - roosters can be very affectionate & they don’t have lady’s problems (egg binding, lacking nutrients due to egg laying etc).
I am deeply bonded with my rooster flock - they follow me around the farm like dogs and often check on me at the entrance to the cabin (they know they are not allowed inside).
My birds are pretty smart too - in a few weeks after my cockerels had first seen sorghum, they learnt to peel the skin to get the grain inside. They have also found a way to hunt for the worms in the sweet potato field - by looking out for yellow leaves with holes, then turn those leaves upside down. Of course, those are totally another story ..