How much to feed?

I just found out one of my cats has gallstones, an ulcer, and other digestive issues.  I am going to need to feed her separately from the other kitties to give medication.  I have always free-fed.  How much do I feed each cat?  I have three cats:  one weighs 14 lbs, one weighs 16 lbs (Maine Coon), and one weighs 8-9 lbs.  I am feeding them dry food although I may need to switch the kitty with the issues to wet food so I can sneak in Pepcid like the vet suggested.

The one who has the issues weighs 14 lbs and may have fat around her heart (we're going to a specialist Wednesday about all her issues), so should I feed her less than the others?

Did your Vet suggest any of them need to lose weight?  When you see the speciailist on Wesnesday, you should probably discuss food at that time, not only WHAT to feed, but the amount of calories.  That's the whole issue with "how much" is calories, just like with us humans.  And those can vary vastly.  AND, the amount of calories per cat can vary vastly depending on their age and activity level. 

Maybe these articles will help you:

http://www.thecatsite.com/a/how-much-food-should-i-feed-my-cat

http://www.thecatsite.com/a/transitioning-free-fed-kibble-kitties-to-timed-meals

http://www.thecatsite.com/a/transit...-to-a-new-type-of-food-canned-raw-or-homemade

http://www.thecatsite.com/a/choosing-the-right-food-for-your-cat

Good luck with your ill cat.  You might want to ask your Vet about compounded meds, if you're not thinking about trying to pill your cat.  Pepcid is very bitter, so mixing into food doesn't necessarily work.  We had it compounded into a liquid that was tuna flavored, but even then the pharmacist warned is it would still be slightly bitter.  Some of the time our old guy would eat it mixed into a bit of food, and sometimes he wouldn't.  Now we just found out it's injectable, so just ordered it that way for our old girl (also compounded)