The group option needs to give the group leader the option to allow the players to enter their phase. What this means is that the all of the players who join the group become phased with the group leader. The group leader makes all the decisions of the quest, and the group members can see the actions that the group member makes. The group leader and members are leveled to the difficulty level of the quest. The difficulty of all bosses and enemies of the quest are multiplied by the number of the members in the group. While in the group, group members can see quest givers, but cannot accept any quest; only the group leader can accept new quests. The group members will have the option to leave the group at any time, but all quest rewards will be forfeited if the quest isn't complete.
Any group member who has already completed the quest, or hasn't finished prerequisite quests, will just tag along with the group leader while he does the quest line; this group member will not receive any quest points after completing the quest, but will receive gold and loot for helping the group leader.
Any group member who has not done the quest, or has started the quest in his phase, will receive the quest and skill points, and loot for helping the group leader. The outcome of the grouped quest will over write the group member’s previously phased version of the quest since it was not completed before the member joined the group.
Note that ALL quests segments could be grouped using this method even the single player boss quests.
Rich