Hi and Welcome to YT!
Your girls are both very small- too small to breed. With yorkies this small, you risk serious and expensive complications including death to both mom and babies during birth.
There is no benefit to your babies have a litter- if you spay them now you will reduce future risk of mammary cancer as well.
Spay your little girls and enjoy them.
We would love to see photos... I am sure they are adorable
