How to Kill Friends...

There are multiple ways to achieve the endings. The guide sections outline the most expedient ones, but I didn't want to leave these particular stones unturned. You can find this stuff yourself from just exploring, but this page is intended to steer you in various directions that you can try out.

Laura

East Bathroom: when Jennifer pauses in front of the door the first time you near it, enter the room and open the shower curtain.
Sitting Room: If you've seen Anne die, check out the suit of armor in the corner to find Laura's corpse.

She's fairly easy to save. Simply walk past the East Bathroom in the beginning and never inspect the suit of armor in the Sitting Room.

Anne

Courtyard: head into the North Hallway (East) from the East Corner. Find the hotspot on the mound of rubble and click on it to have Jennifer collect the Sharp-Edged Stone. Use the stone on the crack in the wall and move through the widened hole into the Courtyard. Just walk to the left until you see Anne drowning in the pool.
Grand Staircase: run past the East Bathroom after Jennifer hears a weird noise and enter the Grand Staircase room. Scissorman and Anne will fall through the skylight.
South Hallway: After seeing Laura die in the East Bathroom, shake the Scissorman pursuit. Enter the South Hallway and you might hear a scream coming from outside. Examine one of the windows and you'll see Anne thrown through the window of the Study.

She's fairly easy to save. Witness Laura's death in the East Bathroom, then just ignore the scream in the South Hallway.

Lotte

Cavern 1: Walk all the way to the right once you get past the dog, and you can witness Lotte's final moments (and get a hint for how to defeat Scissorman)
Shed: Get trapped in the shed. Don't unlock the cell door, but instead wait for Lotte to rescue you. She will be shot by Ms. Mary.

You cannot save Lotte. Her fate is sealed, and her death cannot be prevented.

... and Influence Endings

Ending H

Anne or Laura die, but not both.
Use the Car Key in the Garage to start the car and escape. You'll have to try that three times before Jennifer will work up the courage to abandon her friends.

Doesn't matter if it's Anne or Laura who dies, just has to be only one of them.

Ending G

Anne and Laura die.
Use the Car Key in the Garage to start the car and escape. You'll have to try that three times before Jennifer will work up the courage to abandon her friends.

Not much in the way of notes. Just see Laura and Anne both die and then run away.

Ending F

Anne or Laura die, or both.
Do not talk to Lotte in the cavern.
If Lotte was killed by Ms. Mary in the Shed, do not read the books on the desk in the Mural Room

The key to this one is to not know that you need to turn on the clock mechanism. The only ways to get this information is by talking to Lotte in the Caverns, or by reading the books on the Mural Room's desk if she is dead.
Reading the books on the Mural Room desk will not matter if Lotte is still alive. She must have been killed by Ms. Mary in the Shed, or the books will be useless.
- In other words, if you read the books in the Mural Room, don't have Lotte rescue you in the Shed, and ignore her in Cavern 1, then you will still get Ending F.
As a fun side note, once you get this ending you can select Continue on the main menu and the game will load up in front of the elevator in Cavern 3. You can run out, talk to Lotte if she's there, then run back to the elevator to get a different ending.

Ending E

Anne or Laura die, or both.
Do not get captured by Ms. Mary.
Do not talk to Simon Barrows.
Do not find your father.
Talk to Lotte in the Caverns or read the books on the Mural Room Desk
Take the elevator to the third floor.

Fairly straight forward. Just avoid any of the story beats and enter the caverns.
As a fun side note, once you get this ending you can select Continue on the main menu and the game will load up inside the Elevator. You can select the second floor and get Ending D.

Ending D

Anne or Laura die, or both.
Do not get captured by Ms. Mary.
Do not talk to Simon Barrows.
Do not find your father.
Talk to Lotte in the Caverns or read the books on the Mural Room Desk
Take the elevator to the second floor.

Fairly straight forward. Just avoid any of the story beats and enter the caverns.

Ending C

Anne or Laura die, or both.
Get captured by Ms. Mary, or get into the Shed.
Talk to Simon Barrows.
Talk to Lotte in the Caverns or read the books on the Mural Room Desk
Take the elevator to the second floor.

If Lotte gets killed by Ms. Mary in the shed, make sure to read the books on the Mural Room desk.
If you use the Copper Key to escape the cage before Lotte arrives, make sure you talk to her in the Caverns.

Ending B

Anne or Laura die, or both.
Do not release the crow in the Cage Room.
Get captured by Ms. Mary, or get into the Shed.
Talk to Simon Barrows.
Talk to Lotte in the Caverns or read the books on the Mural Room Desk
Take the elevator to the third floor.

If Lotte gets killed by Ms. Mary in the shed, make sure to read the books on the Mural Room desk.
If you use the Copper Key to escape the cage before Lotte arrives, make sure you talk to her in the Caverns.

Ending A

Anne or Laura die, but not both.
Release the crow in the Cage Room.
Get captured by Ms. Mary, or get into the Shed.
Talk to Simon Barrows.
Talk to Lotte in the Caverns or read the books on the Mural Room Desk
Take the elevator to the third floor.

If Lotte gets killed by Ms. Mary in the shed, make sure to read the books on the Mural Room desk.
If you use the Copper Key to escape the cage before Lotte arrives, make sure you talk to her in the Caverns.
If you forget to release the crow, you will get Ending B.
If you do everything correctly, but go to the second floor, you'll get Ending C.

Ending S

Anne or Laura die, but not both.
Release the crow in the Cage Room.
Do not get captured by Ms. Mary, or get into the Shed.
Do not talk to Simon Barrows.
Find your father in the Hidden Room.
Talk to Lotte in the Caverns or read the books on the Mural Room Desk
Take the elevator to the third floor.

If Lotte gets killed by Ms. Mary in the shed, make sure to read the books on the Mural Room desk.
If you use the Copper Key to escape the cage before Lotte arrives, make sure you talk to her in the Caverns.
If you forget to release the crow, you will get Ending B.
If you do everything correctly, but go to the second floor, you'll get Ending C.

Watch Anne get thrown through the window. Make your way to the Study and pick up the Lantern, which does not appear on the desk if the window scene does not occur. Find the Library, then use the Lantern on the large crack to find the Copper Key. Now if you get captured by Ms. Mary, you can escape the cage before Lotte shows up and spare her life for a little longer.
Watch Anne get thrown through the window. If Scissorman chases you into the Study, you can escape by leaping out of the window and into the pool.
Check out the mirror in the East Bedroom. This could give Jennifer a chance to preen, but there's also a chance for two spooky things to happen.
In the Entryway, you can run around on the second floor and see a portion of the floor collapse.