Or you try this:
1: Go to variables, create a new variable based on "Player Group"
2: Set the variable to something like (Player Group(Player 1(Red))), this allows you to set players that are in range of the NPC giving you the quest, or players who has a specific item etc.
3: Once it is set, pick the player group (Player Group - Pick every player in <your variable> and do (loop actions))
4: Create the quest.
5: Now create a Custom Script (Custom Script - Destroy PlayerGroup(udg_<your variable))
6: (or you can empty the player group).
7: Done.
Now, why use Player Group?
With this, you can also add special effects etc to the player.