Son's right against father

I am inderjeet from delhi and wants to know some way-out for sister's family. Her Name is Saroj and was married to Mr. Mukesh (Nand nagri-Delhi) in 1988, within first year of marriage, she lost her one leg in family violence, after this incident both husband and wife got separated from the joint family and after one year, she gave birth to a baby boy (Satveer). My mother took the baby to my village at age of 6months, and satveer was living with my parents till when he was of 20 yrs. and after this Satveer is wandering here and there, his father(Mukesh) never allows him to stay with family, at present my sister's family is of 2 son's and 3 daughter's, elder daughter left house, two years back and that girl is also begging for bread. Mukesh and a mechanic and he drinks regularly, which is the main cause of the violence in family. Now 6months back, Satveer has done marriage with Priyanka with the help of court, earlier it was going to be an arrange marriage between the family but mukesh demanded a bike as dowry and good reception, which led to the break of the engagement. After the breakup, satveer and Priyanka used to talk over phone continuously, which later on resulted into marriage. Mukesh was not in favor of this marriage but he desired that Satveer should get married to a girl, who was the daughter of a mechanic, works with Mukesh but Sister's family denied this because Mukesh was in affair with that girl's mother. Now Satveer is not having any place to reside, and came to his home with his wife but Mukesh is not allowing them to stay in house and stating that if they will live here then I will not live in house. now what are the legal rights of son, so that he can use and live with his family.