This was a really creepy story and what made it so creepy was that the supernatural part of it was so well into the every day life of the family.

David's confused and terrified but he doesn't dare to tell his family because he thinks that they'd consider him nuts or hysterical then and treat him like a little kid again. He also doesn't tell because he fears the humiliation and embarassment that would cause him.

He tries to figure it out himself but the fear and resolve he feels to go into his room makes it hard for him. The Bible he "uses" to protect himself against the three ghost appeared to me like adapted from horror films. I think it's from those films where people try to save themselves against vampires with hanging necklaces with cloves of garlic around their necks to chase them away. Hm, maybe not the best example, but I'm sure you got the point.

He definitely feels greatest plight when he reveals himself to his mother. He doesn't really want to, everything in him refuses to reveal the obviously ridiculous things happening surely only in his overreactive mind. His mother's reaction first seems to prove this as well as David's genuine disappointment that she doesn't believe him mirrors but what she reveals about her own gift (his, only a bit weaker manifestated) really surprises him... I could imagine, and also that he doesn't feel so alone with his gift anymore.

Mom must be some kind of "transmittor" of dead ones who got lost on the way to the Light (heaven?) It's somehow using that someone's there when one oneself's ready but lost the way.

You pictured the three intruders rather detailed. Somehow they reminded me of the inhabitants of "Our little Farm" . Where they killed however in the time frame I think they were or earlier? I don't know, sometime between the 19th and beginning 20th century?