Have you tested him for genetic diseases or other problems yet? I'd worry that if she lied about his weight, what else would she lie about?
Typically, the rule for weight is 3 times the 8 week weight, so you're probably going to have a good sized yorkie, 10-11 lbs. You never know though, maybe he just had a growth spurt, and his weight gain will slow down.
Good luck with the new little one! I can't wait to see pictures!
