I'm so sorry to hear what is happening in your chapter, PM_Mama.
I'm not sure what your Panhell's rules are on adding new GLO's, but my college rules stated that another group could not colonize or form until all houses were at quota. It doesn't sound like that is the situation on your campus.
So maybe your ex-sisters are just barking up the wrong tree with their idea? If they want to make Greek Week more interesting, it might help if they could get their organization recognized by the campus.
It kind of sounds like maybe these girls just want more attention because they weren't in the chapter for a year.
Keep us updated. I hope that everything works itself out with minimal drama, of course.