Well I don't know anything about how your sisters evaluate rushees for selection (nor should I), but I would assume that just "meeting the requirements" is not enough to get into your sorority. Personality and the ability to fit in with the other sisters is likely to at least be a consideration. In this situation, you are actually a blessing to your older sisters. You have witnessed these young ladies (if you could call them that) in a setting where they were obviously not on their best behavior, and perhaps letting their true personality show through. So through what you've seen and experienced, you can help them to (again) make the right choice in not selecting these girls as new members.
Of course, courtesy and friendliness during a rush party are always appropriate. Don't act like you don't know them, and try your best to be nice... but don't be completely fake either. By behaving in a polite and cheerful way, you will come off as a class act, no matter what their behavior or response might be.
And if, by chance, the other sisters disagree with you and your org. decides to pledge these individuals, look at this way. Sisters don't always get along... but you will still share a special bond
). I heard some of them could be trying again, how do I act like I never met them? When I think about it-it seems really hard, I mean these girls said some nasty things and formed clicks (sp?) that picked on some other pledges. . .how can I let them in even if they meet all of the requirements? 
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