We just entered the multiple Yorkie world this week. We introduced our 3 year old Spicy to new pup Lucy on neutral territory. Lucy wanted to play but Spicy wouldn't even look at her.
We are on day 3 now and its much better....Spicy has learned to jump on the couch when he wants away from her. Lucy still tries to chase Spicy to play but instead of just being scared, Spicy is starting to have some fun with her.
I think we are on the right track...but like everything with puppies...it takes time.
It's this potty training that is getting me....I had so forgotten how hard that part is!