Hi Kingius Returns
This is a scripting question and best answered in the script forum.
But to help you out, place your doors as normal with the different names (e.g. doors 1-3). Then place a single "triggerzone" covering all doors. Name the zone something like "openalldoors"? Run this script in trigger "main"
;Triggers
:state=0:state=1
:state=1,activated=1:activateallinzone=1
;End of Script
noticed the "activateallinzone"
Then for your switch that can open "all" doors run "switch.fpi" for its "main" and type in the name of your triggerzone (openalldoors) in the "ifused" field. Done.
Hit the switch and all doors should open

best luck