ok im sure at least half the people that play this game have wondered about this. mainly i think this would affect parkour and sparring. just imagine the insane tricks you could do with a third person or the epic fights where its a free for all or even perhaps a team deathmatch

Not possible because it would cause too much lag, I believe this used to be possible, I can't remember though.

i dont see how its much different from any other multiplayer game

Has been suggested multiple times and has been turned down every time due to the drawbacks of implementation.

Please read the rules and search whether a suggestion has been made before you make it.