Harassment by elder son on my father's self owned property

My father is a senior citizen and living with me (younger son). My father had one son and two daughters from his first wife. I (son from second wife) have a elder brother who abandoned us 15 years before after his marriage. But just 2 years before when my father sold some property for paying off some debts, my elder brother started demanding money from father. My father denied of giving any money to him as he sold the property for the purpose of clearing the liability. My father had already gifted my elder brother a flat in Mumbai at the time of his marriage. Now my brother and daughter in law abuse my parents. Even my brother's mother in law and brother in law harass them at the native place. My elder brother has filed a case against my parents claiming his right in the property. But the said property is a self owned property by my father. My basic query is : 1) How can my dad get rid from this harrasments? 2) The buyer of the property from dad is also afraid because of the litigation. 3) What could be done to resolve the case at the earliest? 4) Does my elder brother have any claim on the property? Please Note: Mutually resolving is not possible because we tried talking to my brother but he is showing his excessive greed and demanding for all the property but do not want to take the responsibility of parents.