Not so much offering advice, but I find the title of this thread unfair.

The actions you describe are unbecoming of any Greek organization -- local, national, or international. If this nationally-affiliated chapter is doing what you say they're doing, then it's a problem with *A* nationally-affiliated chapter, not with national chapters.

My sorority is the only NPC on a campus with 3 local sororities. They shit talk about us all the time, especially during rush. While we may be the largest sorority on campus, there's certainly more them than there are of us to cause trouble. That's why I find it hard to believe that this sorority is "terrorizing" the rest of you guys.

As others stated already, you really should get some proof before spouting off and accusing them of being responsible for what's going on. There isn't anything anyone on this board can do to stop the bad things going on -- you really need to enlist the aid of your school officials.