Integrating, what age?

With those ages, it's best to integrate like sizes so I'd wait till the chicks are almost grown. If you have a LOT of space and free range, it can work earlier.

 

I personally would not integrate until the younger ones were close to adult size. It really depends on what your setup is.....The adults will definitely bully them, and chase them away from the food and water. Plus, the larger chickens can injure or even permanently maim the younger, smaller ones.

The last time I had young chickens to add to my flock, I let them free range together, but at night, they each went back to separate coops, since I had two coops. That made it pretty easy, because the bigger chickens would chase the smaller ones, but they could hide. It took a few weeks and then everybody was getting along.

 

I have also integrated mine on our free-range acre of woods. I have three different ages of chickens and they are all doing OK together. Mine are 2 weeks, 5 weeks, and 4 months. The big ones chase and peck at the little ones but the little ones can run away. No chicks have been hurt. I put food in three different places in the yard so the are less likely to fight over it.