I’m kind of surprised at that reaction at those ages, I’d have expected the opposite. Mature hens often beat up on cockerels. But they are living animals, you just never know.
I agree. Let them all out and see what happens. Chickens don’t like changes and this is a change, but they also adapt, sometimes quicker than others.
What I’d expect to happen is that the cockerel will mate with one or more of the hens. That’s how he establishes dominance over them. For him to be flock master he has to be the dominant one, otherwise he can’t do his various jobs. Don’t be surprised if the hens run from him instead of squat and he physically forces them to submit. That is normal when a new rooster is introduced to a flock of hens. A lot of people not used to the process get really upset when he grabs their head. Don’t be. That’s a necessary part of the process.
I’ll add something I wrote a while back on the mating process between consenting adults. It might give you an idea of what to expect. It’s possible yours will quickly go into consent mode but it is also possible some physical force will be involved for a while.
The rooster dances for a specific hen. He lowers one wing and sort of circles her. This signals his intent.
The hen squats. This gets her body onto the ground so the rooster’s weight goes into the ground through her entire body and not just her legs. That way she can support a much heavier rooster without hurting her legs.
The rooster hops on and grabs the back of her head. The head grab helps him get in the right position to hit the target and helps him to keep his balance, but its major purpose is to tell the hen to raise her tail out of the way to expose the target. A mating will not be successful if she does not raise her tail and expose the target. The head grab is necessary.
The rooster touches vents and hops off. This may be over in the blink of an eye or it may take a few seconds. But when this is over the rooster’s part is done.
The hen then stands up, fluffs up, and shakes. This fluffy shake gets the sperm into a special container inside the hen near where the egg starts its internal journey through her internal egg making factory.
