Team game: My initial thought would have been to simply divide players into teams (3 vs 2) and give each player exclusive control of particular unit types of their team's army. Sort of like:
player 1 controls goblins and wolves
player 2 controls archers and orcs
player 3 controls everything else
player 1 controls knights and archers
player 2 controls everything else
And then simply use the existing rules as written.
Really like this! Gonna try one day when all's painted... in the year 2029...