first things first, you seem very emotional(lots of stuff you post on hear seems like your sad) so dont do anything too stupid like stabbing them or anything. If you actually see them throw shit at your sister, first ask your little sister not to talk to them cause that could be a big part of the problem and if they dont stop go and talk to them before you do anything. If they all beat the shit out of you than just get a baseball bat and start hitting themas hard as you can BUT NOT IN THE HEAD. after that they probably wont want anything to do with you anymore so they wont bug you and yor sis