urination and defecation problem

I recently moved in to my sister's house with my 2 cats. She also has a cat who is the same age as mine and a dog. Prior to my moving in she had been noticing that her cat was urinating on the dog's bed. After my cats have been living there (they all get along great), her cat has been urinating in other places such as clothes hampers, the floor etc. This morning we noticed that he also defecated on a window sill and on the laundry room floor. We are unsure as to what to do about this behaviour. Any suggestions would be appreciated.

Thanks :-)

Sarah

First thing you absolutely want to do is have the vet rule out a urinary tract infection. This will make the cat avoid the litterbox and going to the bathroom is painful for the cat. If you don't rule that out first, nothing else you do will matter.

Also how many litterboxes do you have? Ideally you SHOULD have one per cat plus an extra one. Even if some are right next to each other, they need variety and one place to pee and one to poo if they choose to. Cats are picky.

After that you can try different litter also, try an unscented, a natural one, clumping or non clumping...