You're halfway there having a daddy roo. Let me explain by way of examples from my own flock.
One of my "pullets" from an order of Cream Legbars turned out to be a cockerel. I thought, great! I can use him to breed more of them, which I sort of accomplished when I got an Easter Egger /Legbar pullet and an EE cockerel from him, mistaking blue EE eggs for Legbar eggs. (I'm definitely not a breeder.) The flock didn't have a rooster at that point.
The daddy roo took the young four month-old cockerel and trained him, disciplined him, and taught him to be a very nice rooster. I didn't need to do a thing other than to leave the two mostly alone. The only way I can see this not working out in your flock is if your aggressive roo teaches the younger one to be aggressive.
It's turned out that my two are also very good companions because I don't allow constant access to the hens, only limited access to avoid stressing my hens. They do everything together, sharing a coop, dirt bathing, free ranging.
I suggest, if you have multiple cockerels, select the one that shows the least aggression, then give him over to your rooster to do the rest. But wait until he's at least four months old before you do. The timid cockerel won't challenge your rooster, and there shouldn't be any conflicts to upset everything. That's pretty much how it's been between my two for six years until this summer when my younger roo finally challenged his pop and now he's the number one. After the challenge and switchover between them, there has been no further fighting.