What to do, what to do???

Coco is 18 months old and started off on a higher-end canned food (and dry) but didn't really eat it well (along with his companion) and they had diarrhea too, so the vet suggested we keep changing foods to one they'd eat AND would stop the diarrhea (said some foods are too "rich"? for younger cats). They both settled on Sci. Diet "culinary creations", sooooo that's what he's been on for about a year now.

We just got a new kitten, Maggie, (because Coco's companion died) and she's eating California Naturals canned food---and eating it really well and has nice poop, so we don't want to change her. I've tried getting Coco interested in her canned food, but he prefers his. That wouldn't necessarily be a problem except that she seems like she'd like to prefer his too, but I won't let her. It's been easy as the last 2 weeks (since we brought her home) we've kept them separate when we're out of the house and at night, so that's when Coco eats his food--when Maggie can't get to it.

We're now letting Maggie out into the rest of the house for more and more of the day, so now I don't know what to do about the food issue.

Is Science Diet "Culinary Creations" good enough to let them both eat indefinitely? Personally, I've had good experience with Sci. Diet---our last kitty died at age 21 after having eating ONLY SD dry all her life.

I really hate the thought of trying to force a change of food on Coco when he's been through so much the last 2 months--the loss of his mate and the gaining of a new one 6 weeks later.

Any thoughts for me?

Thanks!

Tracey