Agriculture land occupy by unknow person illegally

 sir 

My elder brother having land in mosur at rainepet distric in tamilnadu the land was settle  to his wife  from her mother on 1973  at age of 12year . he got document  from his mother inlaw  just  6 month before , He checked  revenue document  all are changed by some un know person   the land doument also registered by unknow person on 1983 without my brother knowledge. Now document and patta unknow person name only

 Waiting valuable reply 

Thanks

S.Saravanan