My alpha bitch humps my beta bitch when the beta comes in to heat. It's a sign of dominance. I would suspect your other females are showing signs of an impending heat, or signs of dominance that your alpha wants to supress.
He is your friend, partner, defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devot