Hi: I recently switched my cats to World's Best orange bag cat litter made with corn. They weren't wild about it at first, but are now using the box. Here's the problem, they both eat the litter. Is it harmful to ingest?
I've read that there have been issues of mold with corn litter (although not with corncob litter). However, even with daily or multiple times daily cleaning out of the box (pee clumps, poop) there's still a lot of bacterial building up. I would suggest that you obtain a litter they don't eat.
You might also consider adding a box - it's suggested to have one box per cat, plus one beyond that, but of course space can be at a premium.