Brad, Alex, Julia, Conrad, and Fliss are the characters you need to keep alive for this achievement.
This guide is spoilered as it goes through each chapter where you can possibly get a character killed, and how to avoid this. In general, you don't want to fail QTEs - the timer for these can be turned off (single player only) in the Accessibility settings.
I'd recommend going for this achievement *not* on your first playthrough, so you can familiarise yourself with the sections and whatnot.THEATRICAL CUT GUIDE:
CURATOR'S CUT GUIDE:
If you've followed this all correctly, all your characters should be alive and the achievement should unlock post-credits. Please let me know if you come across any edge cases that I've missed out.