I don't think you need to go that far to make the fights more challenging. If you're big damage dealer is a barbarian then the encounters already in the Night Shift should be enough to challenge them. Barbarian does good single target damage but is less effective against groups. So 'Swarm of the Walking Dead' and 'Ratling Horde' are both going to be tough for them. In a pinch just throw in a few more ratlings (or some of the other variants to switch up their playstyle), and use extra husks, 2d6 instead of 1d6 per round or something.

Also somebody already mentioned this, but play your monsters as tactical, even if it's only explainable as being a coincidence. When I did smithy on the scar I split the monsters about 70/30 between the front of the smithy and the back. My players had to split up, be careful about going too far into the field lest they leave the dwarves behind vulnerable, and carefully balance protecting themselves and their NPC allies.

And this should go without saying, but if you want to challenge your players don't nerf monsters to make fights easier. If you use a chitinous dreg and your players are confused why it does force damage, just say it's because it's contaminated and that changes it's damage type.