You have to teach them to go in. I had to teach mine. I also treated them and used a command each time I put a bird in the coop... I use "go in your house". In addition I think others are right the coop maybe hot at night, inside my coop during the summer they do not sleep in the inside spot as the coop needs modification but they are in the caged area. Also they need to feel the coop is their safe space... do not use the coop to force interaction this stresses them... watch some gentle training methods on parrots, many things we do innocently are actually seen as aggression by birds... one is using cages to try and pet birds for example, petting in general. But consider heat issues, treats, roosts (they may not like the roost), ladder into coop, also make sure coop is clean. As to flock dynamics, as long as they are not fighting don't stress about that... pecking order is a real thing and applying human ideals to chickens is not good, respect how they are... they do not think like humans... trying to force them to act how we think humans should might cause fights.