Two Cats, Different Feeding Needs

We have two cats, Jack and Max, who have different feeding needs. Jack is fat plain and simple and was when I adopted him. He also had a urinary issue, so he gets special food, but he is fed twice a day, 1/4 cup, vet's direction. Max is basically a Billy goat and can eat any food with no problems. He is inheireted from our former roommate. She kept him on a free feeder, which we can't really use because of Jack's weight issue. We feed them both the urinary formula food, but Max needs more. Jack detests can food, would adding a little to Max's meals help him gain a couple pounds? Thanks in advance.

Absolutely.  Anytime you add calories, it will help them gain, and canned food has calories