Much of the feeding guidelines depends on size, activity level of cat, calorie count of the food etc. A 6-8lbs cat in most cases should be eating between 5.5oz - 8.25oz so roughly 1-1.5 cans per day the label does give you the approximate amounts based on individual food content.
By slowly increasing the amount of food they're getting from 1 can each up by teaspoons for example you'll be able to see how much they actually need by what they leave behind. By the way you can leaved canned out for upto 8hrs for them to nibble on, some cats like it a bit crunchy.
The amount of water I was adding to the canned was sbout 1-2 teaspoons per meal & didn't have troubble getting her to eatb
Avoid biting when a simple growl will do
The Spirit Lives As Long As Someone Who Lives Remembers You - Navaho Saying
Vindication ~ For all those pets who became sick or lost their lives from tainted pet food