We just got our second (Rexy) about a month ago (Rowdy is 14 months old) and OMG

it is sooooo much easier with the second one. AND the joy you get watching them play together is just awesome. My husband is sick and doesn't feel good much of the time. Of course, he loves watching Rowdy play and playing with him, but I just can't explain to you the delight of watching 2 little guys doing the cutest things together!
It feels like Rexy is potty training himself because he HAS to do everything that Rowdy does. Now, I won't say he never has an accident but they are about 1/10 the accidents Rowdy had.
I think the company thing (having 2 to keep each other company when you are gone) cannot be overstated. Yorkies are such social creatures and to have 2 as companions is enriching their lives, probably in ways we really can't fully understand - but I CAN tell you how much it will enrich your lives! You will be saying, "how did we ever get along with just one Yorkie!"
Just take it from one who has recently experienced the joys of 2 - IT'S GREAT!!!