i'm surprised to see such animosity toward the local... however this is probably due to an altercation that is unknown to you and your brothers- something like allegations being brought up... or the local simply getting more pledges... it varies and as i'm sure you know- girls can get all riled up over little and big things....
so... panhellenic is not just for national sororities but they do have to get voted on i believe- i'm not sure what the rules are here... but i know that we are a member of panhell with sisters on the exec board and we are also members of IGC (inter-greek council) with the fraternities and sororities with members on the exec board. (i'm a local lol) in any case... i think i would see how the other fraternities felt about what is going on- like what russellwarshay said.... also- try talking more with the girls to find out what happened- try befriending one of the local sisters and see how they are.... there might be something going on here that you don't know about... just a thought from a girl's perspective....