Well, this might be unpopular, but I say let them share the same food(AS LONG AS IT ISNT KITTEN FOOD). So as one doesnt think the other gets better food.

Kittens need kitten food up to one year. Taz should not eat kitten food though. It will just make him chunky

Why not try innova evo (for cats and kittens alike) and see if that works. Or atleast try to find a food for both, kittens and cats Hope this helps!