For schematic discovery perks, salvage perk bonuses for schematic discovery stack across all crew members in the active ground party. So, if more than one crew member has active schematic perks selected, those all stack.

These perks need to be selected on the left side of the screen in the perk display window and displayed in the lower right corner of the screen - they are not passive. So, for example, if you have two crew members in your active ground team with enough skill to earn the "OFFENSE FOCUS" perk, and that perk is selected on both crew members, you will have a +10% chance of finding weapon and mod schematics. All 4 crew members would provide a +20% chance.