You do not have roosters and hens, you have cockerels and pullets, unsupervised teenagers with hormones running wild and no self-control. They are at varying stages of maturity so the older ones outrank the younger in the pecking order. There is a big difference in the behavior of mature hens and roosters versus pullets and cockerels. Normally mature birds live pretty peacefully in a flock but getting there can be hard to watch.
The cockerels’ hormones are telling them to dominate the flock, which often includes violence. The pullets may or may not know their role to play in the flock. I doubt the pullets are causing you most of the problems but I can’t be sure. Sometimes one can be quite aggressive. Even if they were all the same age this immature stage can be hard to watch but you also have an age difference in the mix to make it even more complicated.
I suspect most of what you are seeing is one or both of the older cockerels chasing the younger cockerel, trying to keep him subordinate. The younger one is probably not fighting back, just running away. If the older ones catch him they do pose a danger to him, likely trying to peck his head so they can injure or even kill him. It’s not that the younger cockerel is shy, he’s scared to death of the older cockerels because they could kill him.
I don’t know how much those pullets are being chased, especially the younger ones. They are right at the age where they are not yet sexually mature but may be attractive to those cockerels. They won’t know to squat so the older cockerels could be chasing them and forcing them. In those circumstances it has more to do with dominance than sex. The sex act is about dominance, the one on bottom is accepting the dominance of the one on top, either willingly or by force. It’s unlikely you’d be seeing that with older roosters and those 4 month old pullets but you have cockerels instead of older roosters.
So what can you do? One option is nothing. With them free ranging this type of thing usually works itself out with no interference by you. The pullets are not likely to be harmed permanently, although the cockerels forcing them can be pretty rough. Even your younger cockerel is likely to survive but he is in some danger.
Another option is to house them separately until they all mature. This could mean locking up the younger ones, the younger cockerel only, or the two older cockerels. I’m assuming the vast amount of the violence is directed toward the younger cockerel. The older cockerels are not likely to injure the pullets but you are dealing with living animals, no one can give you guarantees. I did ask which older chickens are chasing which younger chickens but you did not answer.
You have another issue, three males and six females. Since they free range it is possible they could all mature into responsible adults and work out how to get along. This normally involves each mature rooster, once they mature, carving out his own territory and keeping his own harem out of sight of the other roosters to lessen potential conflict. Getting there could be extremely rough but since you are dealing with living animals, practically anything is possible. You will often have people give you magic numbers of how many hens are required for each rooster to solve all problems. Some people with one rooster and over 20 hens, even mature ones not adolescents, have problems with over-mating and barebacked hens. Breeders and others often keep one or two hens with one rooster and don’t have these problems. There are no magic numbers that solve these problems for everyone.
My usual suggestion is that you keep as few males as you can and still meet your goals. Having more cockerels does not guarantee problems but it does increase the likelihood of you having problems. With your three males and six females I think it is pretty likely you will have problems. Getting a lot more females is not the answer right now but if you need an excuse to try this you can. Once they mature it will help, but getting them to maturity can really be rough. I don’t know what your goals are or how many chickens you really want or why, but my strongest suggestion is to remove two of those cockerels from your flock. You can keep them locked up in a bachelor’s pad, eat them, or get someone else to take them. In your circumstances that’s what I’d do, but I don’t know your goals.
