Ok - I have a few ideas.. here they are:
Is Sinatra feeling ok? (vet visit if he's not).
What is Sinatra's breed? Is he Siamese or even part Siamese? I had a Siamese for 18 years (he lived to 18!) and he'd wake up EVERY NIGHT at 4:00 am and meow like crazy. When we moved to a time zone 2 hours away, he then meowed every night at 2:00am like crazy. It was just his thing I guess. He was fine. Siamese is a loud breed of cats.
OR, perhaps he needs some play time before bed. Give him lots of toys like fuzzy mice to bat around. Or some catnip in a place on the floor for him to go & rub on when he's bored. Or perhaps he needs another cat to keep him company. (I'll bet your brother will like that advise, huh?
) I have 2 cats now (along with my 2 dogs) and they keep each other company.
Cats supposedly sleep like 18 hours a day.
OH! Here's another thought ... is he Neutered yet?