I don't think you can compare horse behaviour and chicken and I suspect there is no more thought going into his mating than it's here ill mate with it, just gotta work out how. The crowing is probably pure coincidence, and her broodiness has nothing to do with hearing it. I'm in suburbia a long way from roosters crowing and they still go broody at the drop of a hat. I also doubt the age or tom boy ness of the girls is even a factor other than because they are higher on the pecking order so he has to show he is boss as well before mating so he's not only working out what to do but mounting a hostile takeover from bottom of the pile for top flock position. As for his brother, when I got rid of my rooster I thought the girls would miss him. Don't think they even noticed lol. I think you are giving him far too much credit for rational thought .
Its my first experience with roosters, I'll admit. I have found breeding males very similar so far across species. He certainly seems smarter than my ducks, no offense to them!