Can you put his husband's parents stuff in a storage? As far as cooking for him, he is 17! My kids eat what I make, I don't offer restaurant service in my house. Doesn't he know how to make a sandwich or a bowl of cereal if he is hungry? As far as the trash in his room, just shut the door and stay out of there than you don't have to worry about it. When he gets sick of the mess, or the fruit flies, he will clean it up. It is his mess, let him do it. You are NOT his maid and he is old enough to take care of himself, so let him.
Does he respond to his dad the same way? He may be depressed, but you are still providing for him and if he can't treat you with any respect, he needs to know that is NOT acceptable.
My kids are 13 and 14 and since they were very young, they learned that we all help clean the house, we all help prepare meals, and we all talk respectful of each other. They even do their own laundry and clean their rooms. ( I don't have to make them, they do it on their own) If he didn't learn these things when he was younger, you can't expect for him to act any differently now. I would stop with the separate meals, and if he doesn't like what you are making, he can make himself a sandwich or eat what you prepared. Let him be responsible to eat, he isn't a little baby or toddler. If he is THAT sick, then he needs to be in a mental hospital or a nursing home.