I had a lot of dominance problems with my yorkie when he was younger. Try reading up on establishing a pack leader and hierarchy. For example, have your kids and husband feed him, always have him work - do a sit or something - before he gets his food, never free-feed him, but leave his food for 15 minutes and if he doesn't eat it, take it away until the next meal.
I have had many problems with my yorkie coz he is a dominant, assertive little guy who doesn't know his size. I had him socialized and trained and although this helped, he still 'attacks' our other dogs (we visit my parents regularly and they have two staffies
).
My sister's labrador has been living with us for a year and although they were used to each other, there was a dominance thing coz they are both boys. What I did is always feed the labrador first - he is older - to establish him as the leader.
When the yorkie bites, yelp like a puppy would do - this helps for me.
Sorry for the long post, I know what you are going through and hope my advice helps you and your family.