J.C.
I have cats who used to have problems with going in the litter box. Upholstery cleaners and carpet sprays with the oxy clean stuff in them really help. I like the advice you got about separate litter boxes. If you could do that, it would be great. Something that also definitely works excellently is a cat litter called Cat Attract. It has things in it that smell nice for the cat and since I started using that about one year ago, my cats always go in the litter box. Cat Attract can be found at Ralph's supermarket or some pet stores. Best of luck.