Guppies (Poecilia Reticulata) belong to a different genus of fish than platies (Xiphophorus variatus) or swordtails (Xiphophorus helleri) and thus are unable to breed with guppies. There is the potential for guppy/molly breeding as both belong to the Poecilia genus but I havn't read anything about attemping that cross.
Platy/swordtail interbreeding has been long established and is a generally accepted practice.
Platy/swordtail interbreeding has been long established and is a generally accepted practice.
