guppies pregnant

I have three female guppies, two look pregnant how can I tell which one is giving birth? We found one baby guppy in the tank and wondering also about how long will be between the birth of each guppy ?? Thanks !! Lowri

These two guppys have been getting larger and larger. I know the black one is pregnant but the orange one I am not sure because the gravid stop isnt dark. What do you all think and what is the time frame you all give each of them to give birth. :) I am having issues loading the pictures sorry...