How often and how much should a cat eat per day?

Cats will usually self-regulate and eat what they need, so you should just make sure they have food. A cat that gets fat is probably not getting too much food, it's getting the wrong kind of food.
A cat should, when standing, have an outline like a race track when seen from above (straight sides and rounded ends). If it either narrows or widens toward the back end, the cat is too thin or too fat respectively.
Cats will usually self-regulate and eat what they need, so you should just make sure they have food. A cat that gets fat is probably not getting too much food, it's getting the wrong kind of food.
A cat should, when standing, have an outline like a race track when seen from above (straight sides and rounded ends). If it either narrows or widens toward the back end, the cat is too thin or too fat respectively.