This is so awesome! Golden Axe has always been one of my favorite beat 'em ups... I hope you people manage to finish this.
Or a exclusive three player mode?
You know, there isn't one single beat 'em up for any console before the PS2 (and it is the PS2; the DC doesn't have any) which has a three or more player mode in its main game. Guardian Heroes (Saturn) has a six player battle mode, and The Peace Keepers (SNES) a four player battle mode, but neither game supports more than two in the main game, and no others do either.
I'm sure it'd be difficult, particularly on a 4th gen console, but someday someone should correct this problem.