I brought home Casie because I think a second dog does add value to Scottie's life. Even if he seemed to hate her a lot at first. Dogs love company and I just couldn't stand leaving him home alone every day when I went to work.
When they're home now, all they do is sleep. But just knowing someone else is around is comforting. I didn't want Scottie to be home alone and depressed. Hehe..
Not to mention, Casie has the energy to play chase and steal toys with Scottie a lot better than I can.
I do think the older they get, the harder it may be to become accustomed to a new pet at home. I would assume it's just a matter of time though. With your case, it seems your Yorkie has always been in the company of other pets, so it shouldn't be a problem!
**So excited for you that you adopted your new baby! I would also take them out for a first walk together. I also did the slow transition when bringing Casie home. I monitored them a lot before letting them spend time together under my supervision. Enjoy this fun time!!