Registry made by someone to cheat us in 1993

Sir, History of My House: We are living in a small rental home since 1968. Previous owner final a Deal in 1993 for sale that home with us in just Rs.20000/- deal was final and my father gave him token money through legal agreement.But my father borrowed money from a friend.On registry time father's friend told to my father that he will manage all legal formalities so don't worry.That day was some problem in court so registry can't made but father's friend made power attorney without inform to my father.He got power attorney in favor of himself.My father had no information about Power attorney.Friend told to my father that when my father will return borrowed amount Rs.Twenty Thousands to him then he will give that power attorney documents to my father.But after few months when my father asked to him for return power attorney and get his borrowed money back.My father's friend gave excuses and passed two three years.Then my father hired an advocate and sent summon to him.In court he presented registry in his favor so Judge decided that we will give him rent regularly but he can't get home from us without any legal reasons.Since 1993 we are depositing rent in court because my father's cheater friend never asking for rent because rent is only 30/- Rs. Per Month.But now he is demanding 5 Lacs for that house as per market value and we have only 3 lacs to give him and he is not aggree to sell that house to us in 3Lacs .We can't remake that house as per our need.1st of all he is a cheater so I want to teach him a Lesson. Question: Please suggest me what should I do against that cheater and what are legal rights to us.