I am not sure exactly what 'synced up' means here, its ambiguous with all the options you have. If you want to see all the quests your group members have one one carbonite like pane of glass. If you want to know whats left for the group members for each zone (or entirely) If you want to level them all through the zones of quests and don't know the lowest common denominators, etc.

I would use a carbonite clone, with a multiboxer tour guide. I would also load up wowhead client quick to track what is left someplace easily (i find wowhead easier to use than the in game stuff).