You need to advance the main story to the point where you found the chest in the hidden dungeon in Sunee (Dorgania) and talk with Lucilla in Minsk Harbour about it.
Once you're at that point in the story, Eloen will stand near the entrance of Ebron and talk with a male elf. Talk with her, and then re-enter the map, so that her location changes to stand in front of the storage building on the left side of Ebron. That's where the foursome scene will trigger.