If he's 2.75 lbs @ 22wks I'd imagine that he'll keep growing. He'll at least grow until he's 8mos old. Stewie grew until he was about 10months old, then he leveled off and even lost some baby fat and got some more muscle.
Do you plan to stop your other dogs from playing with your Yorkie forever? I would try to socialize and teach them early. They probably have a grasp on how small he is and will be gentle. It's Preston who probably doesn't realize how small he is
