The fat one gets only wet (vet’s orders, she’s semi feral and she hunts rodents and may have a second family who feeds her) and the elderly underweight one gets all the wet food she’ll eat, then is offered dry food as a treat. She prefers dry, so she’ll have some even though she’s not hungry.
They both get a slurry of nutritional yeast and hydrolized collagen powder in water for dessert.