The cats will go just right outside or go upstairs and make a mess
Hi John, sorry you are having problems with your wife's cats. First I would have them all checked by a vet to make sure they are not ill. Be sure the litter boxes are kept clean and add a couple more so they each have their own. If they go upstairs, clean the area really well and add a litter box where they make their mess. Good luck. Cats are wonderful creatures and sometimes certain things unknown to humans will set them off.
You need to have a litter box for each one
And you still might be able to train them to use the toilet, with some patience and dedication.
Have more than one litter box. Empty the wastes daily.
Keep the clumping litter at least three inches deep, adding fresh litter on top after you scoop at least every other day. Cats can change their litter preferences so change types. After a few years my 2 cats rejected crystal litter and now only accept Nature’s Miracle clay litter.