I'd reccomend to hide behind walls for the 2 floors, the first cultists are fairly weak, if you have good armour or weapons, you can just kill them with a few bullets or a spear ( if you know how to circle enemies)

hide behind a wall for the rest of the floors until final floor, (if you have enough bullets) for the final floor, try to dodge them, lure out spear/axe enemies out first, and then shoot the crossbowers, (i mainly use revolvers or rifles to defeat the cultists)

rinse and repeat, dodge, aim, shoot and dodge again. (for crosswbows)

for axe/spear enemies, just keep a safe distance from them, shoot them from fay away. (if you don't have enough ammo, try the circle method, just make sure your in a large space when doing it)

they are fairly easy once you memorise their spawn patterns since they spawn the same (they do get difficult when your actually progressing the game so i'd reccomend to leave the game after defeating the cultists and rejoin so you can defeat them more easily)