First off, I only feed my guys 1/2 wet food and 1/2 dry food...
Mine will eat about 1/2 a 6oz can each... Which is about 1, 6oz can a day IF I fed only wet food. Now, it depends on the kind of wet food...The can should have a reccommended amount on it (i.e. 1, 6oz can a day per 8lbs of weight), etc. But usually those recs. are for a fairly high energy cat. The better quality the food the less you feed (i.e. if you are feeding a grain free can like EVO or Wellness you'll feed less than say a can of friskies). I'd start with feeding 1/2 a can 2x a day or 1/3 a 6oz can 3x a day and see how much they eat. If they are leaving some, just take it up and feed less the next meal.