I have two suggestions that could maybe be helpful for grouping with friends.
1. have a ??? item in each zone. In Final Fantasy they had this as a goblin footprint. This footprint would let you scroll through all cut scenes in that zone. So in theory you could resee all you did. In addition there would be a npc bard that could erase a title you got from completing mission. This in theory could let you redo it with a friend or so on.
The other one, give everyone five rings. These rings could be given out to special close friends. These friends could help you out on any quest.