What is the punishment for physical assault/battery?

My father and 3 other family members were attacked at home by 10-15 people at night. As my father lodged a complaint against the president of a village in Visakhapatnam for his illegal acts(secretly selling sand from river, selling govt land to people in the village without NB registration etc), the president came to our family member's house at night where my father stayed as a guest, and started slapping him. After 5min, he left and he sent the people who he sold the govt land and the people who help him with sand smuggling, and the mob stormed the gates, came into the house and started punching the men and women including an old lady. They dragged my dad and one more guest on to the road and started kicking. Both my dad and the other family member are left with bruises all over the body, fractured wrist, swollen dace with black eye. In that condition, the people along with the president dragged my father to the Panchayat office and threatened him to sign a withdrawal letter from the old case(sand smuggling etc). Yesterday, the local sub inspector came to the village, asked a few questions, took pictures of my dad and other family member and told us to come to the station the next day to sign the FIR. He didn't even go and meet the president even if we complained against him. I would be grateful if you all experienced lawyers here suggest what should be the next course of action? How can we make this guy pay for the crime and the damage he did to our family? What are the IPC sections that fall into this category? This guy has a lot of political connections and thinking he can get away with all these crimes. I understand that sadly court needs solid proof, so what can we use against him in the court? Thank you in advance.