Welcome to Pet Talk catwhisperer. I'm sure you'll love it here. I also have three cats and one of them has a slight weight problem. I feed all three of them a weight management formula and I measure the amount I feed them. Pepper is the one with the slight weight problem. He's 17lbs but he's a very large big boned cat. I used to worry about his weight but he was very sick last year and lost a lot of weight. He was only 12lbs and I could feel his tailbone. I think his ideal weight is about 14-15lbs so he's not too much overweight. Feeding them in different rooms and measuring their food is a good idea. If the cat is very inactive then they don't need as much food. Good luck.