Disociating myself from my mother? What about my sisters?

If you can afford it, take advantage of modern technology and put them on a phone plan with you - a cheap phone without internet accessories can run just $5 to $10 / month extra for each of them. It will help you keep in touch with them on an everyday basis. You cannot allow your mother's chaos to continue to rule your life, but I think it is great that you want to throw your sisters a lifeline, and that may be the best way to keep out of the everyday chaos, but still be involved every day!