IMPORTANT: The main walkthrough includes some general notes about this achievement/trophy. If my tactics aren't working for you, there are many other approaches on YouTube.

Start by reloading your save from the beginning of the level. Or, load any Home Sweet Home save, let Lara die, then press Action/Enter to open the Passport menu. Page to the right and choose "Restart Level." Save the game during the cutscene showing the cultists' vans arriving. Then press Look to cancel the cutscene.

Immediately side flip to the right, over the bed.

Then roll...

...and jump/run forward to the keyhole. Use the GUN CUPBOARD KEY to unlock the door.

Now grab as many supplies as you can before the first 2 enemies with bats (1-2) arrive. I'm sure you'll find your own method, but I had good luck going for the ammo pile in the middle first, then the pile with the SHOTGUN. If you jump directly onto the first pile and hold Action, Lara will start the pickup animation as soon as she lands.

Next, quickly pick up the small medi pack and 2 large medi packs. (You can ignore the flares as long as you get the other ones, as shown below.)

If you take the large medi pack near the edge last...

...you can then side flip left onto the other shelf. Sidestep left and grab more shotgun shells.

Lara may automatically pick up the nearby flares at the same time. Otherwise, step back and grab them. You'll need at least a few flares to light up the BALLROOM.

Finally, hop back and grab the last pile of shotgun ammo, but only if there's time. You'll have another chance later. It's OK if you take a few hits, but try to get out of the closet with at least 3/4 of your health.
NOTE: I'm not numbering the pickups, since you probably won't get everything on this run anyway, but if you gathered everything in the closet except one pack of flares, you should now have the SHOTGUN with 74 rounds, 1 small and 2 large medi packs, and 6 flares. If you skip the last ammo pickup, you'll still have 54 rounds, which should be more than enough for now. You'll have a chance to return to the closet later. You'll also get another small medi pack and more shotgun ammo from enemies (below).

Run/jump past the 2 bat guys, out of the closet, and around the bed to the bedroom door. Take running jumps when practical to cover ground faster.
NOTE: Some guides recommend approaching the windows to get the attention of the gunman on the balcony (counted below). I would suggest not doing this. He'll probably notice Lara anyway, but if he doesn't, there are suggestions for dealing with him later.

If things are going well so far, save in a new slot. Then run out the door.

Turn left and follow the landing forward...

...then right, toward the top of the stairs.

Jump over/past any enemies you encounter on the way.

At the top of the stairs, veer right...

...and take a running jump over the railing...

...to land on the tiled floor in the entryway below.

Immediately roll...

...and run forward into the BALLROOM. (Don't jump until Lara has moved under the archway, or you'll risk banging her face on the wall and getting stuck.)

Light a flare and heal if necessary as you run into the BALLROOM and around to the right, to the button on the wall.

Press it to turn on the music. Save again in a new slot if you like.
NOTE: After the Challenge Mode update, pressing the button activates the music only once. When it finishes playing, pressing the button again does nothing. But as long as you turn the music on before killing the first enemy, and lure each one to the BALLROOM before killing them, the achievement/trophy should still unlock.

At this point, you should have 5 or 6 enemies breathing down your bathrobe: The 2 guys with bats (1-2), a 2 gunmen (3-4) and their dog (5), and possibly the gunman (6) from the upstairs balcony. Draw your weapon as you hop/backflip away from the button and start shooting. Try to kill the gunmen first while evading the enemies with bats and the dog. This isn't always possible, but do what you can.

Use the open space to backflip away from pummeling/biting enemies...

...and flip side to side to minimize damage from gunfire. When this first group of enemies is dead, heal if necessary. And save again if things have gone well.
DARK MODE: I plan to add optional dark mode for these pages, but my current priority is updating the walkthroughs. Meanwhile, may I suggest a reputable dark mode browser extension, such as Dark Reader? (Download only from trusted sites, like darkreader.org or your browser's official add-on/extension site.)
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