Ah, ok.
Eight weeks is the minimum age for integrating younger birds with the older ones. But they need to be able to see each other through a pen, or dog crate for a few weeks so they can get used to each other first. When you integrate them you can leave the pen or dog crate open so the younger ones have a place to hide away if they are getting picked on. You aren't supposed to interfere with any squabbles between the birds unless there's blood, or one of the birds is being brutally mean; otherwise the squabbles would last much longer.
Once the older birds have astablished dominance, then everything should be peaceful. If there is one peticular bird that is being brutally mean, separating that one from the whole flock for a few days so that it can't even see, or hear the rest of the flock should calm the bird down. I put my younger birds in a smaller pen that's inside the bigger one. When they are older than 8 weeks I just put them in the pen to eat since they're not eating the layer food yet, then I let them out with the rest of the flock.
At night I just let them all sleep together in the coop since there's not as much commotion at night. I put the big birds on their own perches, and the younger ones on theirs. After some time, they didn't really mind each other. The ducks seemed to get along fine with the two new Pekins I added; there's not much ducks can really do to hurt each other anyway lol.