Can't do the Gaunlygrym quest

sigmaice

So, I'm not sure if I'm just not able to accept the quest to choose a faction, but neither i or my guild leader can choose a faction after we've accepted the quests. all that is said is it is too late to join. What time do we have to wait till to join a faction? Do we need a 5 man party with guild mates to join a faction?