Hmmm....
I honestly am not any sort of multi-dog household expert or anything...hah aha, but I'm going to just throw some things out there.
Gauge is...9 months? It could be that he is starting to be a "man" and losing the puppy priveleges that he previously had. The other boys are telling him "Hey. You're not a baby anymore, now act like a big boy and don't P*SS me off! Oh, and get off my mom. You don't need her anymore, you aren't a baby, now go away."
He's not neutered, right? I only ask this cuz I know you're planning on showing him. That could be another thing. At his age, he's definitely going to start smelling more like a man if he isn't neutered.
I wouldn't worry about it too much, especially if Grey and Zeus are neutered. They'll probably work it all out.
But, like I said...I'm not any kind of expert...these are just my ideas.
Good luck...you're an awesome doggie mama and I'm sure you're going to make it work and get all those boys happy and lovin' each other again.