I agree with the cat sitting idea..just to see how he is around them.
Put the cats food up and the litter box, maybe in a room your yorkie doesn't go in to?
I believe, correct me if I am wrong, but male cats mark their territory also..ugh..So if it were me, I would go to the animal shelter and pick out a cute girl kitty..LOL
I think that most animals can get along together pretty well as long as they are introduced to each other slowly and they each still have their own "space". Especially your yorkie in this case...his house, his family and all that, LOL
Let us know what you decide and how you went about it, good luck!
