I would suggest using packages to handle this. In your quest, create some aliases for your bandits. They should fill when the quest starts, assuming you point the aliases at the specific references. Then, use the appropriate AI packages to have them stand their ground, move in to attack, so on. Conditionalize the packages in the aliases package stack based on the quest stage. You can advance the quest stage by using trigger volumes.
Package names forthcoming, trying to fire up the CK.
Edit: For the archers, the HoldPosition package template is nice, as well as HoldPositionWithTravel (to give them a small amount of mobility), as well as KeepDistanceFrom (to just try to keep them away from the player). Maybe give those a shot?