Welcome aboard! Friend of mine has guppy tank where they breed like crazy. Good thing you got 2 females, I heard that one of each sex can stress poor female put to death. Those guppy boys are very active and full of testosterone
In my friend's guppy tank there os no breeder boxes or anything. You can see babies of different sizes all over the tank which leads me to believe that if there is plenty of room for everybody to swim, lots and lots of places to hide (live plants being best choice) and if you don't starve your fish, most of your fry should survive unless there some weak ones. And I agree that guppy babies are VERY FAST swimmers
good luck!