He'll probably outgrow it. He's probably very happy to have playmates. Different things work with different yorkies. Sometimes rubbing a bit of bitter apple spray on their snout will, after a few times, cause them to stop a behavior such as this. Somebody on here says to grab them by the scruff as their mother would do and shake them (not too roughly) but use a forceful voice and say no. I'm not much of a disciplinarian, so thank goodness I've never had to be tested to a great degree.
I've been pretty lucky in having fairly well-behaved puppies.
