This frequently happens, what was enough room for chicks, rapidly becomes not enough space when they grow. Almost always, not enough space turns into aggressive behavior. I am making a giant supposition that you got those birds as chicks, and they are about 10 weeks old? (I realize I could totally wrong) But my idea is that this is going to get worse instead of better, as they still have more growing to do.
Even with plenty of space to roam in during the day, winter is coming and with it long, long nights where things are tight in a coop often times for more than 14-16 hours a day. Lots of time for things to get desperate for a lower bird.
Some people try pin-less peepers, it might help you buy some time. If one or two of those birds are roosters, you really need to make some decisions. Roosters need more room. 2 roosters to 4 pullets is very problematic.
I wish I could give you some better, or more easily done options, but you either need more coop space or less birds.
Mrs K