Not sure about the guppies and platies, but guppies and mollies will interbreed. Endlers Livebearers will hybridize with guppies as well. Posted via Mobile Device
Practically any type of livebearer can interbreed, guppies with Endlers, mollies with platies, platies with guppies, etc.
Not sure about other fish, other than as long as they are the same species even if it is a different breed its possible
i know that B.splendens can by mixed with several other species, such as B.imbellis, B.mahachaiensis, and B.smaragdina. hybridisation with B.imbellis is actually the most likely hypothesis for how we got metallic bettas today.