Alcoholic Mom. Any advice?

I need some advise. I'm afraid I will probably be burying my mother in the next six months if I don't do something.... I'm just not sure where to start. Growing up as a child my mother never touched a drink, in fact she was completely against it as my stepfather drank enough for both of them. In 2002 my grandmother passed away and my mother took it really hard. She still hasn't gotton over it. She began to have a drink but only every now and then as she worked full time. It was moderate back then and controlled. Fast forward to 2011, my stepfather was diagnosed with terminal brain cancer and let's just say that now her drinking is way out of control. The doctor gave him 5 years from the time of diagnoses. He is still living and my mother has been taking care of him, if you can call it that. Her work schedule is 2 days on 2 days off and now it's getting to the point where there's not many days on. The days she is suppose to be working she has a caregiver looking after my stepdad and the days she's off she is suppose to be caring for him. My mom is 59 years old with high blood pressure and high cholesterol. Her father died at 56 with a stroke. To put it in perspective, in the last 3 days she has polished off two bottles of wine and a 40 ouncer. She is swallowing downers on top of it. She's not in the state of mind to care for anyone, not even herself and of you seen her appearance she totally looks the part of a drunk. She is not showing up for work because she is two hungover and the caregiver won't report her cause she's to nice. I feel stuck in the middle of it. I'm afraid if I don't do something I will be burrying her before my stepdad. Can someone give me some advice?