Traumatized Puppy- Part II

Thanks to all who had suggestions regarding our new puppy's hatred of his collar. We got him a loose fitting harness and that seemed to do the trick. So he now is able to wear something we can walk him with (eventually), and he is not screaming and cowering.

But now we are back to his "no collar personality". His sister, the pug, who is only a month older, seemed to undersand his problem with the collar, and was very understanding and compassionate towards him. They played and nipped at each other like normal puppies, although the mini pin, would do so in a very submissive posture while wearing the old collar. Now his problem seems to be that he is too aggressive. He loves to bite our hands and anything he can get his mouth on. And when he plays with her, he is too rough, to the point where she cowers and has to get aggresive and show teeth just to get him to remove his teeth from her head or neck. They got along great and cuddled before, with the old collar, but with this new harness, he is a real handful.
I believe he can be a good dog with the right training and patience, and hope it isn't too late. How woud you go about correcting his behavior. I don't think he is a mean dog, he just doesn't know that his play is too rough for the other puppy. We really want them to get along, be happy together, and fit in with all of us.

Thank you again.