I had a nice long lovely response typed out. I also have a new, young, formerly feral cat who's clamboring around my desk loving on me. Say hello Kerry, tell the nice people you're sorry!
Anyway - we have 7 so I understand the problem.
We fed Yittle our diabetic primarily Fancy Feast or Whiskas moist food that was under 10% calories from carbs. He got fed as often as he wanted which ranged from 6-12 times a day depending on what point in his life as a unregulated diabetic, regulated diabetic or diet-controlled remission diabetic we're tallking about. The more in control his blood sugar was the less he needed. We'd feed him 1/2 can of FF each meal or 1/4 can Friskies/9lives.
The other 6 got fed 1/4 can Friskies or 9-lives twice a day, or sometimes some leftover Fancy Feast or Whiskas. They also got Iams Multi-cat with Chicken dry food which is 25% calories from carbs. We would feed them the moist, then after Yittle ate his and left the room we'd put down the dry and wait for them to eat. We then picked it up and kept it out of his reach. He of course found stray kibbles from time to time but thats pretty hard to avoid and it didn't stop him from ultimately going into diet-controlled remission (no insulin).
Now that Yittle has crossed the Rainbow Bridge due to cancer, we're feeding the 6 plus the new formerly feral cat the same Iams food plus their 2 meals of moist food a day. Getting some of ours to even eat moist food at all was a struggle and a half. Tailte in particular, she'd throw tantrums when we tried to wean them all off kibble... she'd slam doors, bang furniture, throw stuff it was like having a toddler in the house. She's the main reason we had to give in and work out a way to feed them kibble. I'm just happy she'll eat some moist, because she's my Zaftig girl and if anybody will go diabetic in the future its probably her. She's in for a rude awakening and kibble-less world if that happens. In fact we tell her - if you want to keep eating kibble you can't ever become diabetic, so she's been warned.
As for the whole quality of the food issue - the one rule we kept was that 1 ingredient of the first 3 ingredients in moist food MUST be a named protein. By that we mean - turkey, chicken, fish, salmon, liver, beef etc... with our finances there wasn't any way to avoid foods that use byproducts and so forth but we could at least insist that 1 of the first 3 ingredients not be byproducts, water or something else.
After that - the first rule of feeding cats is "It doesn't matter what the food is or isn't, IF THEY WON'T EAT IT". You can buy them the most expensive stuff, the best stuff - Lord knows we did for Yittle, he hated all of it. We gave up - Fancy Feast was the highest grade stuff he'd deign to eat. It did the job.