Your real issue is, as has been mentioned above, integration of the little ones. Your older birds are still of an age where they may take great sport in trying to bully the small ones. The little guys need a safe refuge for when they get chased.
Some say to wait until the chicks are almost full size, but I find it easier to integrate them while they're still very young. Give them a week in a safe enclosure in the run to observe the older girls while the older girls become accustomed to them. Then open chick-size openings, more than one for safety, so the chicks can begin to mingle. They'll scoot back inside the "panic room" as I like to call it, when they get chased.
This is also a good place to have food and water for them so they aren't chased away from getting enough to eat and drink. I make the openings 5 x 7 inches so they accommodate the chicks until they're around 10 weeks old. You can also raise the sides of the pen, creating a horizontal opening all around for the chicks to duck under.
This panic room gets your chicks integrated easily and safely while they're still small enough not to pose a threat to the big girls, shortening the length of time for integration.
