Most common livebearers have more problems not breeding than breeding. Basically, if you can keep them living, and you have male and female, then they will breed. Ideally, the ratio should be 1 male per 2-5 females (just like with people
). An 1 to 1 or worse ratio will have the female constantly pestered, likely to death. Also, if these are Sailfin mollies, then 10 gallons is way too small.
Something that just occurred to me - If these mollies are sailfins then they would benefit with 2 ppm of aquarium salt in the water, particularly if your water is soft. (I don't know off hand what that amounts to amount wise or specific gravity wise.). Mollies come from a very hard water environment - not quite Tanganyika, but their habitats sit on limestone shelves, and have a lot of calcium in the water.
If you don't have hard water, and you don't salt it, you can seriously shorten your fish's lifespan.