Here comes the whole poecilidae x xiphophorus argument again!!
What you have is a platy (xiphophorus maculatus) and a Molly (poecilia latipinna).
The last time this came up somebody likened it to trying to fit a square peg in a round hole and said cross breeding them was not possible. However, scientifically and artificially it is possible.
One last thing though, I believe a balloon Molly may already be a hybridised form of Molly and, although they can breed easily, there could be a slight chance of it not being able to physically reproduce anyway like some ribbon finned guppies, etc.