I think two are definitely better than one. I was in doubt about getting our second yorkie, but it was the best thing that I ever did. It is so awesome the way they love each other. They cuddle together, they yorkie wrestle, they keep each other entertained. Some people think that you should get one, then wait a year or two before getting the second yorkie. I think it would be neat to get two littermates at the same time though. You would just have to be consistant with training and have alot of patience. We added Dora a year after getting Missy, and honestly Dora trained almost immediately and Missy still sneaks off to pee on the carpet on occasion.
