I completely disagree that cavaliers are hard to house train. I got Fletcher at 12 weeks old I was surprised when he didn't use the paper in his Xpen area the first few nights. Although I was very strict with his schedule and making sure I took him outside on time AND we have a doggie door he learned to use quickly. Fletcher is 7 months old now sure every dog has a slip up especially when the weather is rotten but he was a snap to house train.
As for the mouthing, snapping etc. do what a mother dog would do: make a loud noise and walk away every time! Problem is everyone (people) in the house need to be on this plan. I had to nag my Dad to get him to stop playing when Fletcher's teeth touch his skin or clothes. Its more people training than puppy training. Also make sure you are always playing with a toy or something else to bite on. After all biting is how puppies play. My middle son is not very good at that he would lay on the floor and call Fletcher to play and have empty hands guess what happened (and still happens) Fletcher bites on his hands or his cloths. My son gets up and walks away which I want him to do but because he doesn't offer a toy or something to play with I think they both end up missing out. Pre-teen BOYS are hard so are puppies its all a learning process.