Just letting everyone know 3 things:
1) If you want to join multiplayer, everyone who wants to play together must have the game open to the main menu, then the host chooses the 'HOST' option, then invites everyone.
2) The jump squares parabola is not 100% accurate :)
3) This should be the best working version of the multiplayer features. Also, added a jump indicator, (other than the bar) which should help your jumping.