Nope...won't work..not even professional cleaning. If they're old, they could have kidney issues or diabetes, or like you say, just senility. I'd have them checked out. Are they going in one particular spot more than another? I just lost my old guy and he had trouble with the litter box and would pee just outside of it. (I have a large closet I use as a "litter box room.") I used the puppy pee pads and placed outside the box and put the edge under the box to hold it in place. He would "go" on the pad and I would change the pad every day.
You will have to replace the carpet but for now you can take up the padding under the "spot" and use Nature's Miracle on the carpet. Even if you can't smell the urine, the kitties can. Nature's Miracle seems to do the trick.
You might want to try a large litter box ...a lower sided, longer Rubbermaid container. Older cats have trouble navigating. If you are using a hooded litter box, try removing the hood. Maybe place a couple of litter boxes in different spots in the house. If you're using the clumping litter, try switching to clay and emptying it totally once a week.
Good luck..it's hard when the babies start to show their age.