I have 4 different hens, RIR, buff orpington, barred rock, and a California white (which I think is a variation of leghorn). They were never aggressive until around the time they started laying. They are using both nest boxes now. But I have also noticed them "waiting in line" or even trying to kick the current bird out. But it seems to be less of an issue now they they have two options.
The two getting pecked at I guess get along alright, I would say they are in the middle of the pecking order. However the top hen and the lowest hen get along just fine. Its weird. I hope that things will even out, but I think my next step will be to separate the dominate girls for a few days. The hardest hit hen seems to be just fine, the blukote seems to be working for now.