I have a little yorkie mix female and recently added a yorkie male. It all depends on the individual personality of the dog and the way in which you introduce them. Bella is very friendly, however, she can be very territorial. She doesn't like overbearing dogs, so it worked out because Rocco is generally very calm and docile. However, if you're not looking to breed I would make sure one or both is spayed/neutered (and preferably both from different breeders). We had Bella spayed awhile back, and after Rocco gets his boosters he will be neutered as well.
Good luck on your search for a new baby!
Having two is a lot of work at first, but I quickly got over the stress of it all..having two is just so much fun!!