In Order to get these achievements you must buy the character that works with the achievement from the Cantina Shop. In order to get all of these achievements you must complete the entire game for the characters to be come available to use. Once you see a character in a level then they are able to be purchased from the cantina (even if it is during a cut scene). In order to get Darth Vader, you must complete A New Hope in the bonus area. Go into Free Play/Arcade/Cantina and choose one of the characters and have a second player choose the other one. Have the character (in this case Vader) stand there while the other character (in this case Obi-Wan) destroys him and it will unlock. This is easiest to do in the Arcade or Free Play (with two people). If the achievement does not unlock, even with doing what it says, try a different version of that character. Obi-Wan has 4 variations, Anakin has 3, Mace Windu has 2, the Love Is… can only be accomplished with the Bounty Hunter Boba not the child.