I wouldn't really consider Malfurion Stormrage a co-leader regardless of how he is labeled in lore. He has never been hostile towards the horde and for all intents and purposes is the leader of the druids, not the night elven people. He does very little (ie, nothing) in governing his people.
Likewise, I would not consider Rokhan the leader of the trolls. It's an unofficial assumption, though may well turn out to be the case. For all intents and purposes, and much to Blizzard's shame as a storywriter, the trolls remain leaderless to this day... that really ought to be rectified immediately.
Lastly, the Alliance does not have a grand leader any longer. Anduin Wrynn is not the High King. The Alliance is now as it once was; an alliance of nations. It does not have a grand leader (and if it did, that grand leader certainly wouldn't be Genn Greymane, either).