The younger they all are when you introduce them, the better off you'll be.
I had 5 girls hatched in March, 4 hatched in June, and 26 hatched in July.  I put the June babies in the coop with the big girls when they were about 6 weeks old.  They were in a wire dog kennel, so all could see and get used to eachother.  After about a week, I let them out, and with just a minor bit of bullying, they all got along pretty quickly.
When the July babies were about a month old, I put them in the wire dog kennel.  After a couple of days, I tied the door so it would open just wide enough for the little ones to get in and out, and keep the big girls out of their feed.  This gave the babies a safe place to get away from the bigger ones.  No one even bothered them, and they all got along beautifully.
When I first let the new ones loose in the coop, I sat in there with them to keep an eye on things for a couple of hours.  I checked them very frequently when I finally left the coop.  You'll need to keep a close eye out for bullying, but that shouldn't last too long.
So I guess the oldest were about 16 weeks when I put the month-olds in with them.  It worked out very well.  I think that was mainly because the older girls were still pretty young.
Good luck to you!