oh dear. get a bottle of hibi scrub from your vets and just keep an eye on the wounds and do the best you can if they get nasty take them in to the vets. don't put any Savlon on them though as it's bad for cats and cause ulcers in their mouths.
other than not letting your cats go out unattended or building them a run you really can't stop them from fighting. just one of the risks you take letting your cat outdoors really.

sometimes i wish they had boxing classes for cats lol... though i have pedigrees now so they don't go out on their own.