Here is what Alex has to do to unlock the endings in the game.

Ending	How to Unlock
"Bogeyman" Ending	Don't forgive your father, don't kill your mother, and don't save Wheeler.
"Drowning" Ending	Don't forgive your father, but do kill your mother.
"Good" Ending	Forgive your father and kill your mother out of mercy.
"Hospital" Ending	Forgive your father and don't kill your mother.
"UFO" Ending	Similiar to the Bogeyman ending. Don't forgive your father, don't kill your mother, BUT do save Wheeler.

Note: This code contains spoilers.