I've been trying to introduce two younger hens (about 2.5 months old) to my existing flock. The existing flock consists of two 2.5 year old hens. For about three weeks they've been sharing a run separated in two. They can see each other all day. At night I stick the younger ones in the coup and they sleep in one of the nest boxes, which is caged in with hardware cloth. Of the older ones, only one is aggressive, the other doesn't care much. I've also tried supervised free-ranging but they seem to just stay away from each other. HELP PLEASE. What can I do?