Conversion of leasehold plot to freehold on Relinquishment deed

My friend's father has 6 sons , their father has expired in 1975 , my friend has relinquishment deed dated July 1996 in which his 4 brothers have relinquished their rights in lease hold plot of their father in favour of my friend and his one brother now they 2 brothers want to convert lease hold plot to freehold plot in their names (2 brothers name) Can they (2 brothers) apply for conversion in their names directly on the basis of their father's death certificate and relinquishment deed ?Actually their father had made will in 1961 on plain paper, which all 6 sons also had signed , in that will their father has mentioned that he has 3 plots of 1800 square feet each plot , plot no 1,2and 3 He has given 3 plots to his 6 sons , means half plot to each son , plot no 2 and 3 have been directly purchased in 4 son's names only by their father Only plot no 1 is in father's own name that is lease hold plot , for that plot only 4 sons have relinquished their rights in 1999 in plot 1 in favour of 2 sons as per their father's will on plain paper and that plot no 1 is already in possession of those 2 sons (my friend and his one brother)since beginning and they have constructed 3 story house on it with their own funds, that is also mentioned in Relinquishment deed Now those 2 sons want to convert lease hold plot no 1 to freehold land in their names , will they have any problem? Will and relinquishment deed, these 2 documents are not sufficient? Please advise