About 8 weeks they will be "fully feathered" and be able to go into their coop. You will definitely have to introduce them gradually to your other chickens. The older chickens will want to show them their place and the pecking order will have to be reestablished. This will mean a lot of pecking and tussling going on and your chicks will still be quite small in comparison to the older ones. There are many posts on this web site regarding ways to do this. One way is to put them into the coop/run inside a wire cage for a few days so the other chickens can see them but not harm them. I think as the other poster said, free ranging them together is also a good idea as long as you are watching them. Then after some time, placing them on the roost at night after all the chickens have gone to bed may work also. Again, you would want to be watching to see how it goes and if it gets too crazy (keeping in mind there will be some tussling going on) and looks like someone is likely to get badly injured then seperate them again. I think it is a gradual process, but with patience can be done successfully. Good luck and I hope all goes well for you!
CJ