sometimes it also helps to look at the thickness of the legs. if the legs look stocky and thick you probably have a roo. if they seem slender probably a hen (pullet). good luck and i hope you really do have a more hens than you think!
Sorry I'm w/ the group that just see one hen, the same one that has been pointed out already. I would move that poor girl out before those boys know they are boys though.
There is a noticeable difference in tenderness from a 2 mo rooster to a 4 mo rooster, just so you know. If you harvest them young, they are almost like a cornish hen. Over one year old and you'll want to marinade and tenderize them bc they really get tough.