Mixed age flock won't get along

Greetings!
I currently have 9 chickens that all live together. 2 are 21 week old RIR roosters and they were raised with 2 other hens of the same age. The other 5 are 14 week old hens. I raised them all from 2 days old.
Once the younger hens were 2 weeks old I introduced them to the older flock by letting them be in the run with them while I as in there with them. When they were 6 weeks old I put them in a fenced off part of the run so the two Flocka could see each other but not do anything to each other. I did that until they were 10 weeks old when I fully introduced them and they were put in the coop with them.
The younger chickens did get picked on to the fullest extent of the pecking order, as expected, and no chicken was ever hurt or bled. I expected this to stop after no longer than 2 weeks, but a month later it is still continuing. The younger hens always stay in a tight group in the corner of the run because if one goes alone, it gets attacked by the older chickens. The older chickens also attack their circle for what it seems no reason. Half of the attacks are just small where they get ran off but the other half are so violent I have to interfere because all four older hens, including the roosters, attack usually one or two young hens. If I didn't break up some of the fights, I'm positive that atleast one of the younger hens would have been killed.
The young hens only separate when the older ones are outside of the run. At night, all the younger hens sleep on the floor until I shine a flashlight in there so they can fly up on a roost when the older chickens are asleep.
I don't know if this is normal and what I can do. The coop is 4x8 feet and the run is 25x25 so I think they have plenty of space. It also seems that the younger hens have no order in their small flock, I never see them showing signs of enforcing the pecking order like the older ones do and their seems to be no dominant one in their small flock. Does this situation seem normal and OK, or is there something else I need to do?

 

Thank you so much EggSighted4Life! I love your name also. When I put them together they all were almost the same size, less than an inch smaller, it must be some hormonal immaturity and lack of confidence like you stated. I'm glad you told me my coop is barley cutting it, I thought it was more than enough! I'll try expanding it or rebuild a bigger one, definitely with more roost space, I only have 10ft right now. I'll also add a third feeder and more brush to hid in.
I'm glad I'm not the only one who has had this. Thank you for helping me, it was worrying to think it will stay this way forever. Thank you again!