My cat is 14 pounds but I have 2 other cats

Hi, so I just weighed my 2 year old cat and she is 14 pounds. Her littermate is about 10 pounds so this feels abnormal. I have 2 other cats in the house, they are all fed with autofeeders but this overweight one tends to go upstairs and eat the other cats' food, so I'm unsure of how to get her to lose weight without unintentionally starving the other two healthy weight cats.