Welcome! I agree w/ cheshire, it sounds as if his problem is not the typical puppy *testing* stage, he seems too agressive. I would seek the help of a certified behavorist, or at the very least get him into a puppy socialization/obedience class ASAP.

Since he respects your alpha dog, he has the possibility of learning to respect you as alpha. It also makes me wonder if you are not firm enough on him, or maybe not being persistant & consistant with training him. Are you alpha over your alpha dog?
good luck with him!