I found the the most difficult part of owning three Yorkies was the grooming. At $30.+ each it adds up quickly and their fur seems to grow at a faster rate than my hair.
We just recently added our fourth member, a Shih Tzu and he too will need regular grooming

but like my DH says, it's only money and we could be spending it on other non-essential things which could be a lot more expensive. Apart from that I found it made very little difference between owning 2.
Walks are never taken with more than two, so I get twice as much exercise

We have a grant old time. LOVE IT...