sry for the problems... I had the same problems... what you need to do is get one from a pet store that looks gravid, ready to give birth... once she gives birth put the babies in a breeder net or get a different tank... they wlll survivr iam sure.... Also, make sure you are properly acclimating her........ Take an air tube, one end in the tank she is going in, one end in a cup/bucket/bag she is in, tie a knot in it so that the water dripping from tank to fish is slow.... do it until her water has doubled.... then take her out with a net and put her in tank (dont put fish store water in your tank).
Same thing happened with me, i had one male that would not die and everyone else did. until one female lived, he died, she had A SINGLE baby, she died, baby lived, got another guppy from a breeder, now i am up to a good60 guppies...... remind you any i got from a pet store did not make it.... not sure why (some got dropsy, etc.). People say guppies are so hardy, but noone remembers there has been lots of inbreeding for color.... non of mine have inbreed AT ALL. i make sure of it. now mine all thrive. To the point that now i must seperate all males and females asap. No more breeding for a while... they can live for 5 years (if properly taken care of)
Also, if the females have had previous babies, somewhere like 3 batches, they typically die to the lack of nutrients and stress labor does to them.