My mother was an alcoholic. In contrast to my AF, she was very a very quiet lonely drinker. She died in a car accident when I was 18 (probably blacked out due to poor health from the drinking). For months after her death we found empty bottles of liquor hidden around the house. I can say that I did not really know her, although she loved us. She was a very troubled woman and I know she is at peace now
I hope you can talk to a counselor at your school, or attend alanon or alateen meetings. Sharing here is great but it also really helps to have f2f with others.
Remember the three C's - we didn't Cause it, we can't Control it, we can't Cure it. Take this message to heart and to your siblings and focus on yourselves.
You mother knows you care for her, but the decision to stop is hers alone.