It's the 501st, the worldwide legion of people that dress up for star wars events and crap. Think of it like the kiss army, except a star wars version, named after the actual legion of imperial forces in the movies.
The 2nd vader is either a decoy, or it's episode 3 vader and old trilogy vader. ep3 vader helmet was made perfectly symmetrical, whereas the OT helmet was a little warped and stuff.
The left has 3 boba fetts, and on the right are (L-to-R) Zam Wessel, Jango Fett, and Aurra Sing, and behind them are 3 MORE boba fetts.
I mean, damn, six boba fetts alone is like the equivilent of 4 nuclear bombs.