I just wanted to jump in and say i know EXACTLY what you are going through....
I have 3 cats, and 1 is overweight. (Ashley) she should probably weigh around 9 pounds and she is at about 13 and a half.
VERY pudgy, because she is a very small boned, petite cat...so almost 14 pounds is alot on her.
Anyway, I have struggled with what to do as well...I also feed Chicken Soup dry, and my 3 free feed. They all also split 1 can of wet food twice a day. My 2 boys are both good weights, although Gaylord is actually a bit thin- but he has always been that way. However, I wouldn't ant him to lose any weight or he would be skin and bones.
I don't want to feed a weight loss diet, because I would then have to diet all 3....I can't afford to go to all wet for all 3 of them, and I have tried that in the past and they hated it anyway.
Anyway, I guess I don;t have any great suggestions for you, but I had to jump in because our situations are so similar
Let me know if you find something that works!