If you want to combine this achievement with the "No Escaping Fate" achievement I have posted a guide here:
All characters except Andrew can die in most encounters with their respective Demons, Andrew can ONLY die in the finale under certain conditions, BY FAR the easiest way to kill all characters is by:
- In "Off Track" make sure to succeed at the Heartbeat QTE as Andrew and keep the gun, the amount of bullets you use DOES NOT matter.
- During the game, be nice to Vince as all characters
- Your actions with other characters in redeeming themselves does not matter
- In "Full Circle" condemn Mary for witchcraft
Mary's conviction will kill all characters except Andrew right at the end of the game, shortly after Andrew will kill himself with the gun, provided you did not spook Vince throughout the game (as he would send Police to arrest Andrew)
Achievement will pop after the House of Ashes teaser.
Comment if I have missed anything crucial, so I can edit the solution.
NOTE: As of right now this method WILL NOT unlock "No Escaping Fate" alongside this achievement.