Sounds like he has everyone well trained. But I think putting a leash on him before asking for something is a good idea or if he catches on to that you would have to leave it on. You could ask him for the behaviour you want and if he growls then enforce it with the leash, like getting him off your dad. Maybe rewarding the good behaviour would help a bit but as was mentioned, at this stage you'll have to be very consistent. You could work with the NILIF treatment also, this usually shows the dog that he is not the Alpha.