Some ideas:
Redecorate his room with his help and use some cool nighttime light features. I am thinking of something like a lava lamp, aquarium, art using dark blue/green Christmas lights.
Would it help if the kids slept in the same room? That and having the top bunk helped me at that age. Maybe set up one room for sleeping and clothes storage and the other for playing/media.
I know a family who frequently have one kid on the love seat in the master bedroom and one kid in the dog bed with the dog on the floor! They don't put them there, they just find them in the morning.
Maybe giving him a flashlight in his bed or let him set up a small tent in his room for sleeping. Maybe since a tent hides you while you sleep, he'd feel less afraid.
Just some ideas.
