How much should I feed my cats?

I read that your supposed to feed adult cats up to twice a day. Well my mom feeds them in the morning (at 7-8 am) then before she goes to work (at 2:30) then I feed them at 5:30 and she feeds them again when she gets home. This has been annoying me for awhile now but my mom won't listen. She gets annoyed because the cats bother her for food all the time so she gives it to them. My one cat is overweight but she acts fine and the other is skinny. So how much should they be getting feed? I also read earlier today that if a cat bothers you for food all the time then they're not being feed enough but if thats the case then why is my one cat overweight?

like people cats have different metabolisms ...

What are you feeding..?? dry / wet both and what brand

how much are you currently feeding??

We feed them wet food and the brand is 9 lives. I usually give them about a spoonful and a little under a half of one. I think my mom gives them a spoonful and a half or two spoonfuls. Sometimes I'll leave a new can out for my mom to give them and when I feed them the next day at 5 she already went through the whole can, so I'm pretty sure she gives them a lot. She also gives them dry food about once a week. The dry food brand is meow mix indoor formula.

One cats eat less of "premium" foods ...

with grocery I would figure 1oz per lb of body wt...