Ok, I just reread what you said, and, I totally misunderstood it at first. But, anyway...I'm glad that Sophie is on her way to recovery!

As for Kirby, he's so young, I don't think he's teething yet...but, it's pretty normal to be mouthy like that. I mean, if he's being mean and agressive, that's different. What I did with Finn was always keep a chew toy (and, I mean always) with me. I would say no, and, stick the toy in his mouth. And, then praise. Another thing I did with Finn was say no, then just fold my arms and completely ignore him. Sometimes even get up and go away. I mean, your dog has to absolutely learn that there is no biting. If there's biting, he gets nothing from you. Don't give him too much attention when he does it. Just a simple, firm no. I think shaking him is a bad idea. Especially with him being so small. Or maybe get a water bottle to squirt him when he does it.

And, even though he's a small breed, please get him some obedience training as soon as they'll let you into the class. And, tons of socializing. It's so important, even with a small dog. Small dogs are actually the ones I usually have a problem with when I'm walking Finn. They're always the most aggressive.

Good luck with both dogs!