When I introduce new birds to the flock, I place them in a separate caged area within the run or pen. I do this first thing in the morning. The older birds will investigate and check out the new birds, but can't hurt them. At dark when the old birds roost I put the new birds in the coop. When morning comes and they all wake up together, it is usually quite peaceful and problem free.
I tried doing that with some young roos I was given but the peace didn't last long when they were in the run together. The roos are getting a little fattening up before they are getting butchered.