Okay, having been a bridesmaid sooo many times, I can say that I may have fallen into that category once before. And let me just say that if I COULD, I would totally go back and get my act together because I think if my BMs acted the way I did, I think I would have a meltdown.
If they have not been married before, they probably don't realize the stress it is on the bride. They don't realize that planning a wedding is SO hard to do alone and by asking them to be in the wedding they carry some kind of responsibility to take the burden off of you. For us as brides, we are so preoccupied with the wedding - sleeping, drinking, eating wedding - sometimes we forget that our bridesmaids only share so much of that.
Maybe you just need to let them know what exactly it means to you to have a bridesmaid, and that it's more than just showing up with a pretty dress on. I know if my friends had said something to me, I would have turned completely around for them because I love them! (I've apologized to them about my behavior in their weddings now that I'm planning my own)
Anyhow, I wish you luck! I know the added stress can't be helping.