Well, I let them all mingle for a bit before separating and locking them up for the night. Five of the six (2 BR, 1 EE, 1 Brahma X, Red Hen and Mean Speckled hen - who will be referred to as "Brunhilda" from here on out) behaved themselves just fine, giving a warning peck when the littles got too close. My EE completely ignored them and refused to go anywhere near them. Brunhilda, however, would randomly chase one down, grab and pull feathers for no apparent reason. She would eat a little, then go running across the coop just to attack one of the chicks. She's an equal opportunity bully, though - never the same chick twice. I finally just got her out of there until I got the chicks back to their own side of the coop and shut in.
Watching that, I thought that maybe she was the top bird in the flock and showing them who's boss. But then I watched as they settled in for the night, grabbing a before bed snack and going to roost. Red hen went to her roost first. Brunhilda followed her onto the roost and promptly got attacked. She went to the feeder. One BR got after her, and the Brahma X just kept crowding her out of her place, eating right where Brunhilda was. After several attempts to get on Red's roost and getting chased off, she went outside. There is plenty of roost space. Red has the one all to herself, BRs roost on the boards in front of the nests and the other three roost in the rafters. So, now I'm thinking that Brunhilda is the bottom bird in the pecking order and just wants to throw her weight around. When I'm home this weekend, I'm considering letting Brunhilda out of the run and locking everyone else in together. Or separating her somehow, anyway, until everyone else is used to each other. I do have a way of isolating her if that's the route I choose to go.