Divorce

Hi, My dad is cheating on my mom from the period they were married, he use to mentally harass and torture her, took all her jewellery and even asked for money from her dad.Because she came from a humble family she didn't courage up to take the effective action then out of fear over lives of her children . She was 17 years old when she was married and my father was 28. She was made to go through mental torture and several domestic torture by my dad's mother(mother i law) Over a period of time we moved out for our further education,(it's been 6 years ) and my mom too came with me to live with us.During that period my dad use to travel with work due to business and work etc.We too never went back, from past 5 years. He use to visit us very frequently.After 2 years recently when he came to meet us , we noticed that he is having an affair with one of our neighbour (divorcee woman).We looked into his phone and found indecent messages.My dad is 64 years old.My mom is devastated by his act of adultery and treachery, and wants to take a legal advice. Having said that I also have a brother who is 28 years old.I am 25 year old girl, we both are not married. I wanted to know what options are available to us on legal front and also after divorce will my brother and me be responsible for my father's take care(including food,shelter and clothing) since he is a senior citizen will he get a benefit of such situation. We don't want to keep associations of any sort with him, due to such stress caused by him.