Divorcing a parent

My father is a retired central government employee and my mother is a housewife. I am a 32 year old woman, unmarried and I have two siblings. Our family is basically a broken family. My father had been harassing us since we were kids but my kept giving him chances, thinking that he would realise his mistakes someday and things will be alright. But nothing changed, he kept torturing us. He didn't provide us with anything. We had to take care of ourselves and also him whenever he didn't keep well. We wanted to put this matter in front of our extended family members to resolve it or just let them know what is happening in our life. But our mother asked us to keep mum so that we will have some respect in the society. We are basically from Kerala and settled in Mumbai. Everyone knows about our family here but way back in hometown, people think that he is the nicest person and we are torturing him as told by him. He is Highly alcoholic and he talks dirty about us. So we basically have an image of prostitutes in our hometown. How are we suppose to go there and answer all their questions and sarcasm. He got some huge amount of money after retirement so he feels powerful now and there are people in his family to back him. We are totally helpless. He is even telling people that we might kill him. So if at all something happens to him later, people will think that we have done it. I really don't know how to go about this. But for sure I have decided that I don't want to call him my father and continue living with him. I don't want to take care of him when he will be in that state later in his life. So I would like to divorce him. Please suggest as to how to go about this.