This movie was never about the twist that the other boy is dead.
The Director did made it obvious at the first place only the brother could see the brother and not anyone else. It was obvious in most shots, so it's obvious the Director wasn't hiding it.
The power of the movie OR if you call it the Twist is that the dead brother appears to be a real Ghost, and not his imagination, and it is reveal at the final act dialogue that the mom was playing along at first to imagine the dead brother was still there, and that got the alive brother confused, and thus he was convinced that the mother was fake, who just had a plastic surgery, who you can tell from the plot reveal that she might have done it due to her insecurity after the divorce and as a not-so-famous tv personality. The "accident" they have been referring at the scene where the mom was talking with the police was indicating the death of the other son.
This is one of those rare movies where I hated watching it at first, because I thought the same, why was it so obvious that the brother is not real, and I surely thought that the rest of the movie was boring because I already knew the twist.
But then i changed my mind at the end, when the movie reveal that Ghost are real, with the wide shot of the mom's spirit walking out from the house, thus the dead brother was real as a "ghost" and not an imagination of the alive brother.
I thought this was unique and brilliant, a movie where I thought I hate, but then changed my mind at the very end, and thought it was a brilliant film. Very rare such feeling I have for a film, thus I think this film is pretty innovative and unique on it's own. Definitely worth more than 6.7 stars! I give it an 8 atleast!