You can also tell them to buy some Cat Attract Litter by Dr. Elsey which they can get at Petsmart. I know it's on the expensive side but it works. It helped me when I was also having inappropriate peeing issues. I just put some of it on top of the old litter that I was using. They may also need more litter boxes. Even though the cats are indoor/outdoor,they may not like using the bathroom outside. They should have at least 3 litter boxes in low traffic places so that they'll have some privacy. Some cats also don't like covered litter boxes. Good luck.:)