joekhoo,
I had my Male Yorkie for almost 2 years, before I got my Female. They've been together for a couple months now, and I STILL can't figure out if he likes her or not !
As DAngel has said, some do and some don't, and I think if I had brought the Female in to the Fam earlier, he would be a little better about it. He was devastated, I think him thinking that She was in some way, replacing him in my Heart. I have had to intensify my attention toward him, in an effort to soothe his apprehension.
They play, run, scuffle with an occasional nip to her neck, to suppress some of her excessive puppyness, but... when I pet her, or come home, and they both are trying to greet me at the same time, His discomfort with her is quite obvious.
Yorkshire (as a Breed) was made to be assigned a duty, and for it/them to carry out that task, without human intervention. I know that sounds a little heavy on the responsibility, but, we did it, now we got to live with it.
That Breeding has IMHO caused considerable individuality in the Breed, and having seen the sides (single dog/a pair/group) I'd say that if he had his "druthers", he wouldn't want anyone around me, except him. Today, tomorrow and forever.
My Male and Female are Brother/Sister but several Liters apart. At times, I can see a natural "Love" being established between them, which is why I selected a Female for his companion. Soon, I'll have the Female altered, and with that, there may be a change in this situation.
I don't know if it's just my stubbornness, but, I think in the long run, that him having a Breed companion is the right thing to do.
Gees... I sure hope I'm right.