Fatty liver may be related to his diabetes and diet.
Addressing fatty liver is often by adopting a low carb diet, and strictly avoiding added sugars and fructose (high fructose corn syrup), as the fatty liver is contributed to by his liver having to handle the carbs that are eaten.
He will need to be advised by his dr on the kidney stone and whether it requires treatment or is just an incidental finding and be safely observed. Certainly ensuring good hydration will be a start.