I had the same problem when I had 4 cats. One got huge. he lived to be about 14 but I am pretty sure he died of complications from diabetes. He was healthy until the end and I knew it was the end so there wasn't anything to do about it by that time.
One thing I did the last couple of years was just to pick up the food at certain times of the day so at least he couldn't eat all day long. The others got used to coming when the food was down, like early morning and afternoon. I always picked it up at night.