I don't really have a way (or the space) to separate them out in the main coop -- it is only 6x8, so space is pretty much already designated. However, when everyone is in the yard (most of most days), they are all sort of together with just wire between them.
Sharol, not sure if your setup will allow this but what I did was setting up a section with just the chicken wire in my main coop. I let the 5 to 7 weekers in the small sectioned off area and block off the entrance. The bigger birds will gawk and check them out but can't hurt the little ones. After a week or 2, I just let the little ones out the same time I let the rest of the flock out. I have done this 3 different times and seemed to work. I do leave a small entrance for the smaller chicks to run back in when the bigger birds peck at them. For the most part, they figure things out on their own. Since you have a bigger yard with a smallish flock, I think it will work for you. I don't recommend just putting them together without the slow introduction though unless you can supervise closely. Hope this helps.