Hmmm perhaps it's a mix of NPC location order and which one is on the tile first?
Maybe as a little test done on a backup of your project or something:
1) set up a map to use 4-5 npcs, maybe all main character npcs to help determine who's on top
2) have a standing Namingway chillin nearby. Add movement commands to his "if No" box so you can just talk to him and watch the npcs walk to the same tile ingame
3)????
4) PROFIT
Disregard steps 3 and 4, I coudn't help myself with the Suth Park reference.

As an alternate test, you could try having said npcs already set to the same one location and unactivated, then set up namingways "If no" box to activate them all simultaneously. That might help clue you in on what's going on!
(Meant to reply to this days ago, but it's been too hot for me to do a whole lot on my computer without getting half a headache. Sorry 'boot that.)