Always leave wet food out for free feeding (can out ice pack underneath), unless you're trying to guide the curve (which is a slightly more "advanced" topic, can worry about that once you get settled!).
There's a number of reasons for this. If he drops low, it's good to have food available if he needs it so he doesn't go too low. Unregulated diabetics don't process food the same way, and often need to eat more than a regular cat, so this will help maintain weight (unless of course Pookie is overweight). Lastly, one part of the DKA recipe is inappetence/lack of food, so always want to make sure they eat enough.
As for the dry food, there's a few options off the top of my head:
- Shift them all to the same mealtimes instead of free feeding, and feed in different rooms
- Convert them all to low carb wet
They do make smart feeders and pet doors where only certain animals can open it, based on a chip or something in their collar. But I've never been a fan of collars on pets, strangulation hazard/limbs getting stuck.
I'm sure others will be along with other ideas, I know lots of people here have a "mixed population"