People have done this. The species you mention will cross breed. Usually what is done is to put all males of one species in a tank, whit all females of the other species. This way they don't have a choice in mate selection.
Except for sword and platy cross breeding, I don't really recommend doing this sort of cross breeding. You tend to end up with fish that are not very desirable.
If you want to use mollies, your best results will come out of various molly and molly crossings, choosing two fish where you want to combine the traits of the parents in a single fish. You will need to ruthlessly cull the offspring to establish the breeding line you want.