Sandy,

First thing you need to get them checked out at the vet to make sure they don't have UTI's, urinary tract infections. Once that is ruled out, get another litterbox. One box per cat. That's the rule.

As far as getting rid of the smell, Nok-Out is sold online and works great. If not, try Nature's Miracle, sold at any pet store.

If it's a behavioral problem, you can get a can of Feliway. Cats don't mind being in the bathroom as long as they have food, water and a litterbox (or two). Spray the bathroom with the Feliway (follow the directions on the can). It has an enzyme in it that calms them right down and will help of it's a behavioral problem.

I had both problems and that's what I did. Good luck. Let us know how you make out!