I was also worried about my little one because she did not drink enough. It's not as bad as your siamese, but I was still concerned because it's important for her health.

On a hunch, I put a bowl of water and food in the bathroom. She now comes in and drinks water regularly if I'm in there with the door shut.

I think she was unhappy drinking and eating near the other cat.

Perhaps your little boy feels the same way?

Good luck.

PS, you can learn to do the fluid injections at home yourself. Some of us done so for our kitties with renal problems. They are actually pretty OK with it...it's not like a pill.