Westerado: Double Barreled

The achievement is awarded for killing all essential NPCs. The unlock conditions and list of NPCs was fetched from Steam.

Note: There have been reports of progress not tracking correctly, so you might want to keep your achievement tracker open and quit to the main menu before moving to a new screen if it doesn’t track a kill.

You need to kill:

- The brother (Play as the Hero, enable the tutorial and kill him when asked)
- Uncle

Clintville
- Concerned Wife
- Drunk Husband
- Miss Tress
- Old Miner
- Sheriff
- Everyone in Saloon
- Rancher Bell
- The Banker (If you rob the bank you'll also permanently alter the exterior Clintville and remove some NPCs, better to just shoot the Banker for this)
- Teary-eyed Woman
- Undertaker

Clintville Station
- Sister (Have to finish the Train Master questline first to get the train to arrive)
- Train Master
- Ticket Salesman
- All Store Members (Hat Girl , Gen. Store , Miss Store. Make sure to steal a weapon first because why not)

Rancher Cobb's
- Rancher Cobb

Rancher Bob's
- Rancher Bob

Rancher Richard's
- Rancher Richard

Oil Tycoon
- Oil Tycoon
- Oilrig Manager (If you don't kill her when at the Oil Tycoon's, she can be found at any oil extraction site)

Mine Entrance/Mine
- Miner's Widow
- Miner

Indian Outpost
- Indian Chief

Indian Camp
- Chief's Brother
- Iiniwa

Fort Motors
- Lt. Fort
- Gen. Motors (can be found in the small house)

Santa Anna
- Buffalo Express Driver
- Miss Hatt (Haberdasher owner)
- Everyone in Saloon

Miscellaneous:
- Ostrich Gang (all 5 members)
- Director (see The Fourth Wall)
- Beefhead Bulls
- Brit (Cowboy Helper, 1 screen east and 2 screens north of Santa Anna)
- Hailshot sisters (helpers in far northeast of map)

And remember, if you somehow screw up on a screen (the character flees or becomes unreachable), quitting the game before leaving the screen will reset your progress for that screen. Since the game saves progress whenever you enter a new screen.

Whyatt Thrash has an excellent guide, that is in fact accurate.
There are also amazing guides detailing how to find anyone you need.

After three failed runthroughs, however, THIS Guide is to confirm that YOUR bullet must end the co-stars life, NOT simply having the character in question die. This isnt too hard by using the rifle (750$ OR theft at the store in Clintville Station) to shoot through enemies, while positioning yourself between crossfire. Dying or going to the main menu BEFORE leaving a location resets NPCs in said area.

You MAY also have a problem with, in no real order;
Your sister / Train not showing up. (1)
Indians/Fort Motor lt. / general. (2)
Oil rig manager. (3)
Ostrich banditos. (4)
Miss Tress (5)

(1) To ensure total carnage, You want to start with getting a rifle and taking out the beefheads. After that, get the train running. Random NPCs dont always spawn to help so go to any rancher for more hands. You need this done quickly, if you kill any helper NPCs OR have no quest to turn in to progress time, you cant kill your sister.
(2) Clearing the Fort will sometimes fill it with indians if their quest is even started, so kill the Chief WITHOUT talking to him, go through the pass, kill his brother, go left one screen and kill the indian who gives the buffalo quest.
The next step is CRITICAL. Go to Fort Motor and kill the LT. FIRST. Its best done during her speech as shes identical to the other woman. In my experience shes run off if shes the last alive, where the GEN just sits inside the fort.
(3) Shes the woman talking to the oil tycoon when you first meet him. Shoot them both during the first meeting.
(4) You find one of the banditos in the desert southeast of Santa Anna Station. Out of the 5, he is the only tricky one. You need either an axe to hit him, or a rifle to shoot his hat off. WARNING as if a bandit/scorpion gets him, OR he runs offscreen, your tracker might not register.
(5) In my experience, if she runs off she wont show up at any of her other spawn points. Kill her at Bobs, preferably BEFORE Bob as he wont run off.

Hope this helps someone! It takes about an hour as you will most likely reload a time or two but with the proper setup it isnt hard!
Happy hunting (>*_*)>

For anyone having trouble with this not unlocking, I may have a remedy. My achievement tracker was stuck at 97% and refused to go any higher. Even after around 10-15 playthroughs and being absolutely certain that I had killed every co-star. So if you are in the same dire despair that I was, attempt the following:

1. Delete ALL in-game saves.
2. Go to the home screen and hit the start button on the Westerado game tile.
3. Choose the option Manage game & add-ons.
4. Once in that menu, go to Saved data and choose Delete from everywhere.
5. Delete the game and re-download it.
6. Start a new game and the achievement should pop during the end of the intro, right as you are chasing the buffalo out of the gate.

Hopefully this works for you as well as it did for me. Good Luck, and Happy Hunting!