Welcome to YT! You will get all the info you will ever need here!
I have two girls, and have always had two yorkies at a time for many years. They keep each other amused, learn from each other, and are very good friends. (now!, lol)
It is a bit more expensive of course to feed and vet care two, but not all that much more. If you have good quality pups with not a lot of genetic medical issues, then your vet care will be routine. I think it's a lot more fun having two! I wouldn't do it any other way!
Good luck! Let us know what you decide!