I've met ringworm and few times and unfortunately have more of a reaction to the ointments than I do to the parasite. Instead, I use a home remedy. I get some petals from a marigold (calendula) and mush them up with an oil like evening primrose pil or some aloe vera and then put the goop on the patch. I put a bandage over the infected area (because, of course, its super contagious) and I usually see improvement in 48 hours. Then red and itchy goes in about 4 days. its magiuc stuff, and works for me.
I also had a friend that put mushed marigold petals on a horse that had a ringie on its leg and apparently it worked... not sure about puss-cats, they might lick it off.
But it worked for me and might be worth thinking about.
You could try putting all their baskets and bedding out in direct sunlight after giving them a serious seeing to with hot hot water. Apparently that helps kill off any mites carrying the parasites. I've also heard that some people put cod liver oil on pets food to help keep their skin healthy and more able to fight off the ringie.
all a bit granny's recipes I know, but maybe worth a go in conjunction with everythig else you're doing!