Hi
I would second what the others have said. The only thing I would like to add is that these juveniles will be getting their hormones now and that changes the whole dynamic of how they interact. Think a house full of teenagers with no adults to keep them in check..... it can get unpleasant. If they are free ranged it will work better, but if they are penned, then if one of them starts getting picked on, they have no where to get away and all the birds will sometimes target an apparently weak bird, just like bullies in the playground. Your problem is too many males and with no older birds to keep them in check, things are going to get unpleasant. Even if the males don't fight with each other, they will competitively mate the pullets and make their lives a misery and risk injuring them. Young cockerels have all the hormones but no technique when it comes to mating, so they will forcefully grab a pullet when she is not ready to mate and hold her down whilst they take turns to mount her. Sometimes the pullet will be so desperate to get away, she will get scalped or she can get leg, hip and back injuries and the stress of being repeatedly mated in this manner will also leave her immune system low and vulnerable to viruses.
In contrast, mature roosters will find tit bits of food for their ladies, dance around them and wait for the hen to squat and invite him to mate with her. By squatting, the hen spreads her weight close to the ground and is therefore more balanced to carry the roosters weight without injury.
If I were you, I would reduce your number of males to one or at least create a bachelor coop and pen for the males, otherwise this may not be the last of the sick and injured birds you need to deal with. The boys should get along fine in a bachelor pad although there may be some squabbles. The pullets will be far happier without them at this difficult age. It is not natural for young males and females to come of age together. An adult rooster would run off the young males when their hormones kicked in and protect the pullets and there would also be mature hens in a mixed flock that could put the young cocks in their place. You need to become the flock leader by removing those adolescent boys and protecting the pullets.
I'm afraid I too think your sick bird may have Marek's Disease and if so, then you need to reduce the stress within the flock, as that often triggers an outbreak of it. Too many cockerels running around creating havoc in the flock is one of the primary causes of an outbreak in my experience.
