Just a little update. I called my vet after posting this frenzied mess above and told him that the Valium was doing nothing. He told me it was okay to up the dose to a full pill rather than half.
Re: The Valium, I too wondered about the appetite stimulant and wondered why he was prescribing Otis that when the issue really seems to be that he wants food. But, I was just so desperate. I'm wondering now if there are such things as sleeping pills for cats.
Last night I tried something different before I upped Otis' dose. I didn't give him any Valium at all but instead loaded his food dish with a heaping amount of wet cat food. I feed them the Evo Ancestral diet so I know it's got all the good stuff and protein that will actually stay in his tummy. He went in to the heap with fervor while I brushed my teeth and readied for bed until he eventually reached this threshold and walked away from the bowl to pass out on the sofa.
In the middle of the night I went to the washroom but checked the dishes and there was still a substantial amount of food left. Miraculously, come 6AM I woke naturally and realised that Otis had not come to meow at our door! I hadn't heard a peep out of him. He was still fast asleep! I didn't hear from him until 6:30 when my BF got up out of bed.
I have not had a straight, meow-free sleep in months and I nearly cried from happiness.
I'm going to have to regulate the amount of food I give them for their "real" dinners and breakfast so that the majority of their meal comes in the form of their nighttime snack. I'll figure it out as I go. Otis is only the most hungry at 4:00AM, so if that's going to be when his breakfast is, then so be it.
Thanks so much for your responses and thoughts.
I'll keep you posted.