Advice on how i feed my cats please

hello,

I have had cats for about 3 years now. We have one that is very heavy and one who is about 1-2 pounds overweight. I was told by the vet to give them a 1/4 cup dry food twice a day. I have done this for the 3 years however they have not lost any weight and they used to be free fed. Our one cat was very little still when we stopped free feeding but our heavy one was already 4 years old. I feel bad because they beg so early i worry i am starving them.

We are having more of a problem with pika in our 1-2 pound overweight kitty. Now she has always had pika but she is chewing plastic way more now ( we took up all plastic she will eat any thin plastic even shower curtains ). She does not mean to swallow she just likes to chew. She gets worse closer to feeding time. She has started the past few months taking out a lot of hair on her legs.

I took the cat to the vet and all he said was it looks like it is the food. I told him we gave them grain free and he said that even picking a cracker crumb off the floor or a chip could be enough for that problem. I am not sure what it is. They get flea treatment, the area is not red or broken. The thing is i am very worried that we can't solve this issue and our very fat cat has not lost any weight. She is on better food and off free feeding. I am tempted to start free feeding again due to all these issues. Sorry this is long its hard to find good information and our vet explain much.