Usually you want a female between 5-7 pounds to show only because judges are reluctant to give female dogs the points unless they know they will be able to have pups. I know this first hand. I had a judge tell me this about my 4 pound female I was showing. She was beautiful, just too small. I kept wishing she would grow though and didn't. She was sold to me as a show prospect and was doing great when I bought her around 5.5-6 months. Then she just slowed down in growing. Yorkies are sometimes hard to judge by as to their final weight. This is why breeders cannot and should not guarantee the pups weight at maturity.
It is also impossible to say that a young pup is show prospect until it reaches the age of at least 6 months - too much can happen while it is growing. I have seen two beautiful parents produce one beautiful dog and the rest not so good. I have seen a straight topline go down in the front at 7 months and stayed that way. You just don't know. You hope for the best. I say this with the best intentions. When I first started, I didn't know either. It takes time, research, and with the help of friends we learn.
Your pups are very cute though! I just love new babies and they smell so special - puppy/baby smell. Best of luck with your new babies.
T.