What are these minifigures? Does someone know what theme or set these minifigures are from?
First one is Ultron Sentry from Iron Man vs. Ultron (76029) set.

Second is a minifigure made with torso and legs from Duros Alliance Fighter, Jet Pack, Minifigure, Headgear Helmet SW Hoth Rebel Trooper, Minifigure, Visor Snow Goggles and unknown head. All come in Rebel Alliance Battle Pack (75133) most likely since it contains all parts and similar head piece seen in your picture.
  
Last one is Aaron - Flat Silver Visor, Clip, Curved Slope and Tow Ball on Back, without the slope and tow ball on the back it seems. It is from Moltor's Lava Smasher (70313)