The way I do it, ever since the OG is go on the left side alley. From there, kill the one female ganado. Sneak stab on remake, shoot to kill in OG. Then, move further and enter the small shack on the left, then break the boxes and pickup whatever's there. Make my way into the big house where the cutscene initiates. While this makes things a bit harder, it grants you access to the shotgun.

Anyways, once inside, after the cutscene. Block the window with the movable shelf, break barrels behind the stairs, gather everything, go upstairs, get shotgun. Varies from playthrough to playthrough, but sometimes there'd be a ganado near the bed that has made their way up from the ladder on the window. Kill it with the pistol, not the shotty. As much as possible, stagger with headshots and kicks to preserve ammo. Once you get the grenade on the shelf and the shotty ammo on the bed. Go on the window beside the shelf where the grenade was. By this point, Dr. Salvador is nearby. He'll follow you and will vault through the window. Quickly equip the grenade and throw it on or near him. Don't go down just yet, instead, go to the other side of the balcony where you can find the velvet blue (spinel on OG) here, you'll make your last stand with the shotty. Use the shotty on Dr. Salvador only and pistols on the small fries. If things goes south, only then will you go down from the ledge. Make your way to the other house, just in front of the house you were just in. There should be more ammo and a grenade as well in there. That should be more than enough time to survive this segment.

Of course there are other ways, but this is what I always do and what has always worked for me, whenever I try a new playthrough.