If I lock a door , npcs that have a package se to go act outside of the door and inside of the door space , woudl they need a special key ? a special package or the engine is smart enough to make them pass throught the two areas without needing one? I talk of a door teleport btw not a normal door that opens and close physically ... .

No idea, but this seem really easy to test. Just use the CoC command to enter an area only accessible by a locked door with a follower in following mode. If it didn't work you don't need to check for teleporting doors. If it does, you could place a lock in Whiterun door and do the same.

If the NPC has a key and "inaccessible" is not ticked then yes, the NPC can go through

I made an alias and I added this script to the door is this correct?

Scriptname Issgardseadragondoorlock	 extends ReferenceAlias     Quest Property Erilarquest  Auto  Event OnActivate(ObjectReference akActionRef) if (Erilarquest.IsObjectiveCompleted(30))akActionRef.Lock()endif  Debug.Trace("unlocked" + akActionRef)EndEvent

?