Question about multiple conditionals with Dual Wield

If I equip a character with two different weapons that both have conditional damage increases, do they stack or does something else happen?

Example: A character dual wielding a Heavy Spear and a Fang

If I now attack an enemy that has both Agility Down and Blindness, do I get both the +100% from Heavy Spears AND the +200% from Fangs, or does it only take the higher one into account, or maybe something else entirely?