I read horror stories about yorkies being difficult to potty train and I still do see a lot of owners online struggling with their pups accidents all over house even as adults. However, my Mike was pad trained at home and has been great with it since 4-5 months old. I've put a lot of work and consistency into it. The only accident he had in the last year was peeing on a new rug we recently got, but it never repeated. He also peed in the elevator after we moved houses once, cause someone left a newspaper on the floor and Mike thought a newspaper makes a nice potty pad lol. Some boys also mark, but luckily we didn't have this issue.
That being said, Mike has a crazy prey drive and some behavioral issues, which we are working on. I have family friends with the sweetest calmest lap dog yorkies, while my Mike is a full on terrier and has quite a character
If I would get him a lil yorkie bro or a sister, I would be more concerned with their prey drive, the possible separation anxiety, barking, very high energy, requiring a lot mental stimulation, as well as grooming and dental care.