For starters, confine him in his own enclosure as Peeps suggested. I think that made a certain logical sense to you, didn't it? By confining him, depriving him of his freedom, you are going to begin to teach him that he is under your control, and that, later on in a few weeks, that you also control his access to the hens.
At first, he will probably be belligerent whenever you go into his pen to feed and do stuff, but this will be the most important time during which you will establish your dominance over him. Try to understand that he will have all sorts of emotional issues, yes, emotional issues. He will be angry, frustrated, impatient, and fearful. Remember he has major trust issues also. He's a stew pot (sorry about the analogy) of emotions. I know this surprises you, but it's precisely why roosters are so darned hard to manage. And remember they're very smart. You need to be consistent and straight forward with him, and very firm.
He will challenge you. When he comes at you take your one arm and push him down onto the ground, holding him down firmly with your hand just behind his head, beak in the dirt. Keep pressure on him until he relaxes. You want to know he's submitted to your control before you release him. If he comes at you again, repeat. You will need to do this for only a few days, maybe even less. A smart roo gets the message fast.
No beating or clobbering him with a 2x2 is necessary. It's far more effective to establish control by humiliating him than by brute force. This is something even a rival rooster can't accomplish. You, as a human, have this advantage over him, and he will be quick to realize it.
I would keep him isolated, but within sight of the hens for at least two weeks before you allow access to the hens, and then do it in controlled measures. He needs to learn the hens are YOURS, and you control his access to them. This will begin to teach him to respect you, while you will, at the same time, be earning his respect.
After that, for the next year, it's reinforcing what you've taught him during the first two weeks.
In your behavior around the flock, make sure it's calm, consistent, no loud yelling, or permitting any other humans to disrupt the tranquility of the run. The grandkids can visit, but they need to be quiet and calm when handling the hens, and they need to stay away from the rooster. He will be learning to trust them, too.
At the end of a year, when you look back on what a hellion your well-mannered roo was when you first brought him home, you'll swear it can't be the same roo.