The other turn in NPCs (Uther, Jaina, Sylvanas, Muradin) only spawn at the entrance of Icecrown Citadel after you have killed the Lich King. (and possibly only in 25 player mode, not 100% sure)
Oh and for the record, just to clear up past confusions in this thread about the
[Sealed Chest]. The source of most players' issues with the quest line breaking is that the chest will only drop from the Lich King if you have
The Lich King's Last Stand active in your quest log. If you turn in that quest without looting the chest you will be unable to get it to drop later.
Vendemiaire: Yes, the chest only drops from LK25. Yes, if you complete it in 10 man you will have to ticket a GM. The workaround is to keep the quest in your log and not complete it until you actually get the Sealed Chest to drop.