Cara, in the first place I would wish for your sisters to not blame you (or each other) for this. I seriously doubt that you are the reason your parents are talking divorce--there are surely bigger issues at the root of this! I know you've been having some problems at home, don't know a lot about what's been happening but I have read your posts & things haven't been going smoothly for you. Whatever is wrong with your parents' marriage is no doubt what is causing the dissention between yourself & your mom--if she and your dad are having problems she will be feeling very stressed, and any little thing with you or you sisters will just be one extra thing that is adding to her stress. It doesn't take much to set someone off when they have stresses from other people/issues--and I think maybe there have been times when you have borne the brunt of the anger your mom was feeling towards your dad. I hope that your sisters realize this and don't say it's all your fault just because they've seen your mom get angry with you.
Please do not blame yourself.
I know it's hard, but do try to be tolerant of your parents' bad moods just now. Try to contribute any help you can toward household chores, and try not to flare up if anger is directed unfairly toward you. Don't take sides--likewise, your parents should not try to get the kids to take sides against the other parent. That is just so unfair. If there are specific stresses--money issues for instance, don't make things worse by saying you want or need expensive items that might create a burden on finances just now. Help where you can, and be prepared to let a certain amount of stuff roll off of you.
If your parents do go through with the divorce, trust me, it's not the end of the world. Been there, done that, though I was a small child when my parents split up. As tough as it was at the time for my mom, it really was the best thing in the world for us. Things work out the way they are meant to work out--I truly believe that--and things will settle down for you and you will be happy again, I'm sure of that!
{{{hugs}}} to you Cara--hang in there girl, keep your chin up & I repeat, do not blame yourself for your parents' problems!