Tea for the Troubled

Day 1 on EU

/way 26,6, 20,1 Archivist Fane
/way 24,8, 17,5 The Countess
/way 27,1, 18,5 Kael'thas Sunstrider
/way 32.8, 14.8 Iven

Day 2 on EU

/way 26,7, 14,6 Simone
/way 27,3, 20,1 Vulca
/way 31,7, 14,2 Laurent
/way 31,4, 20,4 Lost Sybille

So this completes the Achievement for those in EU who didnt complete the quest on day 1 and kept it in log.

A little sidebonus-hint. If you do the assault on alts and Iven is up, go to him to do the "Serve Tea" - He wont get debuff and you can do all 15 on him in a few seconds.

For Tea for the Troubled, you'll need to serve tea to 8 specific people as part of the 15 allies total. You will not be able to see them until you transform into the "vehicle" that is [npc=178181] (29.6, 17.6). These named characters are not up at the same time, so you'll probably need to look for them over multiple days. You can re-enter the Tubbins vehicle by talking to him again. Don't hand in the quest until you've finished, or you won't be able to get the achievement.

Location descriptions with coordinates:

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• [npc=179465] is to the north-west, standing near Prince Renathal and his quest turn-in point (26.7, 14.8)
• 
  
• [npc=179477] is to the south-west, near Malevolent Stygia. She's under the bridge to Calcis, standing against a pillar on the ground floor. Look for the red candles on a rock pile (27.3, 20.1)
• 
  
• [npc=179466] is to the north-east on the ground floor, between the Portal to Torghast platform and the wall (31.6, 14.2)
• 
  
• [npc=179473] is to the west, to the left of Reldorn and the Chaotic Riftstone to the Crucible (24.8, 17.5)
• 
  
• [npc=179475] is to the south-west, near Malevolent Stygia. He's standing under the bridge, to the right of the stairs. (27.1, 18.5)
• 
  
• [npc=179471] is to the north-west, up the stairs on the bridge to Calcis (26.6, 20.1)
• 
  
• [npc=179476] is to the south-east, by Drifting Sorrow (31.4, 20.5)
• 
  
• [npc=179478] is to the north-east, outside the wall. If you run up the tall outcropping of stone, Iven and Zena can be found dancing together at the top (32.7, 14.8)
• 
  

Use these TomTom map coordinates before entering the Tubbins vehicle:

/way 26.7, 14.6 Simone
/way 27.3, 20.1 Vulca
/way 31.7, 14.2 Laurent
/way 31.4, 20.4 Lost Sybille
/way 26.6, 20.1 Archivist Fane
/way 24.8, 17.5 The Countess
/way 27.1, 18.5 Kael'thas Sunstrider
/way 32.8, 14.8 Iven

Good luck!

PSA: Do not complete this quest until you have done the achievement. And when I say "complete", I do not mean turning it in to the NPC and pressing the "complete" button (of course, if you do that you're screwed anyway). If you complete the objectives of this quest (serving 15 npc's with tea) and exit "vehicle mode" despite not turning it in, you will no longer be able to interact with the Dredger NPC to serve more tea regardless of whether you still have the quest in your log, thus locking you out of completing the acheivement that cycle.

Edit: To try to get around the issue, abandon the quest and re-aquire it. Don't know if this will work but you can try. Thanks to the commenters for suggesting this.