one picky and the other a 'hoover'

hi all - i'm more concerned about the picky eater (Luna); if she eats an entire bowl in one sitting (1/2 a small can) then she throws up later but i don't know why. usually i must offer her her food 3-4 times before she finally finishes her bowl.
the other problem is the 'hoover' - Boy. he eats like there's a contest on and i can't get him to slow down; then he goes after her food....plus, he constantly begs.
Luna is rather small - 9 pds, whereas Boy weighs in at 14 pds. i feed Boy a 1/2 small can twice a day, as i do her. am i feeding Boy enough - is that why he acts so desperate?
Both kitties are 5 yrs old (i got them 'used'). i got them last Oct-2010.
pls help answer my queries.
thanks

First I want to clarify: the cans you are feeding are the 3oz ones, correct? And each can gets one total per day?

For Luna it could be that she just has a small stomach and 1/2 a can at once is too much. It'd be better to feed her three or four meals. If she is not skinny, (get vets opinion), then it is fine to continue feeding her one can per day.
For Boy at his current weight, one can is not enough, no. He'll need more like 5oz per day. But get an opinion from a vet on his weight as well. If he is overweight, then you'll need to figure out how much is enough to maintain his current weight and then decrease from there.

Welcome to TCS!

THANK you for responding! i know it's been a while but there seemed to be some confusion as to whether catsite was open any more.

yes, i have tried what you suggested for luna - smaller and more frequent meals. it seems to work. i think also, since she's so receptive to my mood, she upchucks when i'm really upset. but generally, she is doing better.

thanks again!!!