Puppy classes, NOW. Both you and your wife need to attend. This must be a family effort, if you want to aviod problems in the future. He is a puppy, and regardless of breed, needs to learn what is right and what is wrong.
I would keep a lead on him at all times, and redirect him when he gets too rough for your other dog. A muzzle is not a good choice, and can be dangerous when left on. He needs training, and wearing a muzzle is not going to teach him anything.
Now, a question on what you said earlier - you said your puppy listens inside because he knows you can get to him to dicipline him.
What do you mean by that?
Is the puppy neutered? if not - I would be making an appointment now.
Wanting to add in, just because a pup has scars, does not mean he was abused. Puppies get into things, it happens.