Food/water situation

My cat has been through a lot in the past month and a half. Started out of the blue with an episode that showed end stage IV, now he’s down to early stage III and stable.

When eating his renal wet food (Hills k/d), he’s ok with it, but I notice he will lick it up rather than eat, and doesn’t stay at his dish long. It is getting in him, just slowly and there is a lot of wasted food. Not enough for trying to get his weight back up. I have another cat and have to feed him regular food separately. Whenever I open that specific can or pour the bag of kibble, my renal cat comes RUNNING for it and I have to fight him off.

I decided to give him back a few tbsp of the regular wet food to see how he’d like it. He DEVOURED it quickly, eating rather than licking. Afterwords, he was still looking for scraps. I notice too that after I feed my other cat his regular food and then take it away, my renal cat will come looking for scraps of half eaten kibble on the floor.

Is there anything I can do to have my cat return to his regular food, just so he will eat like he should? I know there’s too much phosphorus and the protein isn’t the kind he needs. I plan on trying other renal brands, but his regular food seems like a sure way to ensure he’s properly fed and happy.

I think he’s also stopped drinking water. Water level hasn’t moved in days. I don’t know why though. I give subq 2x weekly and he’s not anemic on his latest bloodwork and he’s still using the litter regularly. I thought CKD cats drink lots of water? The wet food has moisture, but What can be done to ensure he’s properly hydrated?

TYVM!