Hello, I'm relatively inexperienced with chickens and have just started the breeding process myself. But when I asked a chicken store employee how to integrate my younger chicks with the older chicks, she suggested to do it while they are resting at night - they are relaxed and calm. Then watch them over the next day or two, and you will see a pecking order take place. If, however, you find they are being very aggressive and are concerned about the welfare of your chicks, mix some vinegar with water, and go in again while they are all resting at night and spray every last one of them. This apparently is supposed to make them all smell the same, and place them all on equal terms with each other. I don't know how much merit there is in this, but I intend to give it a try.
The idea of introducing them at night is one I've heard over and over again. Also, if you are able to let them live beside each other for a little while first where they can see each other and smell each other but can't touch each other, this might be helpful.
I hope this helps!
