I have three batches of chickens living together in relative peace now.
My laying hens and rooster, my 14 week old BO pullets, and my 8 week old chicks.
Here is what I did. When I first got my pullets I had them in a separate enclosure in the chicken coup. They could go in and out through a little hole in the bottom but it was too small for the big chickens to get through. That way the pullets had a place of safety to run to when they got harrassed. They could see the big chickens and the big chickens saw them and got used to them. At that time my babies were still in the brooder.
When it was time to move my babies out I put them in the enclosure in the chicken coup that my BO pullets were occupying. I closed the bottom opening so they could not go in and out, left it that way for a while.
Meanwhile I sectioned off a part of the chicken run and let that be the BO's space. They could see the big hens and the big hens could see them. At night I made them roost together. That worked out pretty good. Eventually I opened the bottom of the little chickies space so they could go in and out at will.
Now all three batches of chickens are together. Although each keeps company with his own age mates. They seem to have worked out their pecking order without anybody getting beat up.
Good luck in your integration process.