I am trying to find the name of a movie ,
Boy has to brake in to his sisters boarding school after it is taken over by thieves (?bad guys at any rate) demanding large amounts of money from the parents of certain children for the release of the students. NAME THAT MOVIE!:D

I think the movie you are looking for is masterminds.
Masterminds (1997) (http://www.us.imdb.com/title/tt0119630/)