The Rooster is telling her to listen to him. Basically he is in charge. It should settle down once the real pecking order is in place. Yes, he probably will start breeding the hens and it can look a bit aggressive at times. I am sure your young hens are not ready to be bred yet, so do not summit to his attention. It is up to you if you want a Rooster or not? They can be very hard on hens.
You can separate them but once put back in, he will be the same way.
You can separate them but once put back in, he will be the same way.