well for starters...goldfish and swordtails shouldn't be together at all. goldfish are cold water fish, swordtails like warmer water. how big of a tank do you have these guys in? and if you aren't too worried about the fry, just leave them. i have guppies, mollies, swordtails, dragon goby, bumble gobies, and a puffer fish together...my boyfriend calls it "survival of the fittest" i know it sounds cruel, but thats how it would be if they were in the wild. small fish get eaten by bigger fish...thats life. lol
but if you want to keep them you can get a breeding net that sits and the top of the tank, just put an extra air line in there for more circulation. and let them grow a bit.