welcome martha, glad to meet you, the addict in my life is my husband. sorry that your sister is causing you guys so much pain. the first book that i thought about was what was recommended to me here, the book "CO DEPENDANT NO MORE" by melody beatte, i think. maybe if they have internet you can offer them sr, and suggest alanon or naranon meetings.
hopefully you have gone to a few yourself. there is not much more that you can do for your parents, they'll have to find there own way, and except the fact that they have done all they can. your sister will have to save herself. maybe you may have to take a back seat to your parents too, if it will help you to feel a little better about this whole situation. i know how hard this must be for you, but i think that you are doing the best you can right now, just to be able to take care of you. its hard enough to have to watch your sister do this to herself, but it has to be even harded to watch how your parents are handling all of this too. i'll keep all of you in my prayers, and i pray that your sister finds her way soon.