I think you just need to lay it on the line with exec! If they do not want to change, then it will be recommended to HQ that their chapter should close. I know threats are terrible, but it sounds like that is what these girls need!! If there numbers are low and they have problems now...they are only going to continue to get worse! Stand up to them and just tell them- YOU WILL NOT BE HERE MUCH LONGER IF THIS CONTINUES!
Good Luck!