How do I get them all sleeping together?

My 2 chickies (14 weeks old) are now happily wandering around together, freeranging with my 3 ex-batts. Everything seems quite harmonious, providing the chicks stay away from the big girls while they're eating. Nelly ex-batt even let the chicks lie down next to her yesterday for a few minutes. The big girls all flock together and the 2 newbies stay together but they dont mix at all really. They sleep in seperate coops, but I want them all sleeping together.
How do I go about this? Im worried that if I sneak them in while its dark, in the morning, the big girls will harm the babies before I get to let them out.
ANy ideas folks? xx

Well I put them all to bed in the same coop last night, and this morning all seemed ok. The perches were down, so I think there's been a bit of a rumpus, and when I let them out, the babies shot past the big girls as if they couldnt get far enough away, but I cant see any bald patches, or wounds so hopefully, they'll start being friends