Swordtails and platies can cross breed, as can guppies with mollies, but guppies and platies, to the best of my knowledge, cannot as they are not as closely related.
thats a no, i know i didn't think moolys and guppys bred but this i am sure of, they may chase each other around an dcourt juts because they are livbeaers an dthe males are always looking for someone to bother but they will not breed
the only livebearing fish that can crossbreed are a guppy to an endler and a platy to a swordtail!! I don't know why people say that guppies and mollies can crossbreed, because they CAN'T!
Sword tails and platies can interbread, infact there are several members of that genus that can, same with the peocellidae, INCLUDING guppy Molly crosses, they say that there are gupy molly crosses because they bred them, in the early 80's.
The fact that guppies can cross with mollies has no effect on wheather or not anyotwoother fish can interbreed, the two instances are independant .