Crowe isn't really dead.His wife really is just mad at him, but the discovery that Cole really could see the dead made him think he was, putting him under a great deal of stress, and triggering a super power (either invisibility or teleportation).
The Poisoned Girl also saw dead people.She goes to Cole to enlist his help in telling her dad how she died. The only explanation I can think of for her awareness was that she saw ghosts while she was alive, and that grants you awareness as a ghost. It also provides a motive for why her mother killed her: Stepford Smiler Mommy couldn't stand having a little girl who was so... different.
The Suicidal Wife was just insane.Her husband was a pretty okay guy, but she had emotional problems and was paranoid, suspecting him of cheating. She slit her wrists out of anger and jealousy, and the bruise on her face is from hitting herself on a hard surface after she collapsed from bloodloss.
The movie takes place in the same universe as Gunnerkrigg Court.Cole is a medium or guide in training.
It's all a Dying Dream or some sort of Purgatory for Crowe.Cole doesn't exist (or, at least not the way Crowe perceives him). The whole thing was something Crowe needed to do to redeem himself, sort of like how he, as a ghost has to pass on. Perhaps his original patient did not really see ghosts and was just hopelessly mentally ill, but Crowe could not reconcile that and his mind or agents of the afterlife created this scenario for him.
Cole's grandmother died in a horrible way.Fridge Horror of the worst class, you know. All the other ghosts Cole sees had unpleasant and violent deaths (hanging, poisoning, shooting by accident, car crashes), so why does he see his grandmother? Well, because she was murdered or something like that.
The dead spirits specifically targeted and haunted Vincent.They taunted and teased him and drove him crazy specifically to kill Crowe. It was all a gambit to get a psychologist onto the other side because the living psychologists weren't helping the people with the ability to help the dead move on. They were driving people with the gift away from helping the dead move on through medication and/or ignoring the gift.
Vincent is Cole's Father.Sear was Cole's Mother's Surname, otherwise he would have been known as Cole Grey. Both had the ability to see ghosts, the only difference being that Cole didn't express his. The relationship was probably a moment of peace for Vincent, because it kept his mind off not only his problems, but somewhat helped him cope Crowe's refusal to help him further. Vincent expressed his sometime after Cole was born. The result caused Lynn to be disturbed and divorced Vincent. Rather than tell Cole what really happened, the story of him running off with a Toll Booth Lady, was fabricated by Lynn, so to not cause any more trauma to Cole. The evidence to support this is the Following:
The Poisoned Girl didn't pass On.She liked Cole for being kind enough to help her expose the truth about her death and lingered at a distance. She's waiting for his time to die so she could have company in the after life.