If your chicks were purchased straight run, you very well may have adolescent cockerels with some early hormone development. I have had a hen do the mounting of other chickens. I assumed she was bi-sexual, because she was laying eggs, and still trying to mount.
Pecking order dominance usually results with pecking other chickens on head, and not mounting. (at least that is how my flock acts)
WISHING YOU BEST,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,and
