The rocket trooper is "RocketTrooper2Officer"
The info for this NPC is stored in the rockettrooper2.npc file in Assets1.pk3.
To use in a map, use an NPC_Spawner and set the NPC_Type to "RocketTrooper2Officer"
OR
Tick the 'officer' box for the NPC_RocketTrooper entity.
You can point a trigger to more than one thing, yes.
Here, I have two light entitys with the same targetname.
The trigger_multiple entity has a target that matches the light entities shared targetname. So, when I push the trigger, both light entities come on, as highlighted in this video by being different colours.
I'm not sure what you mean by the door thing! You'll have to demonstrate it.