Same advice as for people. Get them off the unatural diet they are on. Kibble is the worst for cats and canned isn't much better. The high carbs, weird ingredients and chemicals in it are what causes it in the first place. Diet change is everything.
Cats need real, raw meat. The things they'd eat in the wild. Not something cooked and smooshed in a can mxied with rice and flour and other silly ingredients.