Hi Priscilla and thanks for this question.
I'm Linda, a small animal vet with 10 years of clinical experience.
Cats urinating outside of their tray is a common issue and one that causes huge frustration and stress in the household.
It would not be unusual for issues to start when another cat is introduced to the home, as this can create huge anxiety and cats won't want to share territory or resources. As this other cat sprayed urine, this will have been incentive for your original cat to mark their territory and may have made them fearful to urinate in the same places as the new cat.
As this issue has been going on for 2 years, I would not expect a quick fix.
Because he is 14, the first step is a vet check. Underlying issues like joint disease, bladder stones and cystitis can all be contributing factors so we'd wan to ensure he has a clean bill of health.
The rule of thumb is that there should be one tray per cat and one extra. This may seem ludicrous, but often cats will 'claim' a tray as their own. So there should be 3 right now.
Trays need to be in areas of the home with low foot traffic, where he has privacy.
Cats are often incredibly fussy and won't use a tray because it is dirty or another cat has used it before them, so keeping the trays as clean as possible will help.
If you cannot do this, I'd invest in a self cleaning tray.
Some cats have a litter preference, so the answer can be as simple as changing the type of litter you use.
As well as the pheromone plug-in such as Feliway that we can use in the home, I would start him on some natural calming supplements such as Zylkene.
Ensure he has all of his own resources and plenty of spaces he can go to be alone when needed.
This means a food and water bowl that are not close to each other or to the litter tray, a cat tree, a scratching post, a window from which she can see the outside world, toys, cat nip, food puzzles etc.
All 'accidents' should be promptly cleaned with an enzymatic cleaner, to eliminate the odour and prevent re-soiling.
We should never tell him off for accidents, as this increases anxiety and makes things worse.
For further reading, this resource is very good:
https://icatcare.org/advice/soiling-indoors/#:~:text=A%20form%20of%20urinary%20tract,urinating%20outside%20the%20litter%20tray.
