When I got my second German Shepherd the two of them bonded big time and my first was never as close to us as he was before. People told us they would bond like that so we knew going in that would be the case.
I don't know about Yorkies since Lucy is my first but because of the case with my Shepherds, I know it may sound selfish but I decided from the start we would not be getting her a playmate. She has brother and sister felines that provide endless hours of fun for her not to mention our own world revolves around her
I'll be interested to hear what those with more than one have to say.