Well if he is 6yrs. old he is a rooster not a cockerel and he IS bullying them. I don't know how long you have had the hen's but if it doesn't resolve in about a week you may have to separate them. He is a mature rooster and he should know how to dominate and control his flock.
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There is your answer, they are the newest two, you have only had them 2-3 months things will calm down given time, he is just testing them, he's lovely by the way so just be patient!