How can I file a criminal case in courts in India?

On 04-12-2016 father (age 82 years ) was alone in the house, got his heart operation done few weeks back. My sister and her husband came evening 6.00 pm to my place after 30 min later started fighting for the dowry money. hitting each other, father try to calm my sister, she push him holding his neck. He got hit by the wooden bed edge (time 7.00pm), on his backside of head collapsed there it self. Even though he fell down she did even give up the fight started hitting my father sitting on his belly hitting on his chest ,and slapping him continuously. I was abroad in Spain didn't know all this after 8 years, I came to know what happen, I want to file the FIR against my Sister and her Husband. What should I do, what all the procedure I need to go through file the case in police station. to take legal action against them, please do suggest me the best way to put up the case. kindly request, appreciate your time and patients for my query. Thankfully MR UTTAM ARYAN