Wow, they are gorgeous. I have never seen any that color before. Are you sure they are actually Swordtails, and not Mollies? They certainly look like Swordtails, but it's hard to say from the picture. Do you have a male with the same coloration?
I had a male of the same colouration who had a long, swordtail like tail.
Unfortunately he died unexpectantly in battle with a male guppy a few months back
Now I have 4 females with no male - I might get another male if they are quite rare.
here are some more images:
as you can see, some are mostly black with white parts, and some are mostly white, with a few black markings
Just get a male and you won't have to make them. Just try and stop them! haha Get a bunch of plants and bunch them together in one corner, or some of those glass rocks. Those make really good hiding places for fry.