Suit filed after ~24 years on a property claiming forged POA

My father (now expired) bought a DTCP approved plot in the outskirts of Chennai in 1991. The payment was financed through a loan sanctioned from his provident fund, after verification of the parent documents by his office (quasi Govt Co.). All the parent document photocopies including the power of attorney given by the land owner were provided by the power agent. On receipt of payments to him the power agent has signed the papers and registered it. After 23 year and 9 months, The Ex-Owner of the property (aged about 82 yrs) has filed as suit claiming that the Power of Attorney referred in the transaction is Forged and does not include the subject Plot No. On Verification of the POA document copy from Sub-registrar office, It was found that Ex-Owner has given power for few plots, which does not cover the subject plot (Other plots are typed post registration) The Encumbrance certificate shows the owner as my father (1991 to till date). The patta was not transferred till date. The plot is lying vacant. No taxes, if any, applicable are paid. Legal heir certificate and Death certificate are available. The suit is filed in a munsif court in my father's name. (Summon just received) Please guide us if the case is tenable after such long time, where the records of payment (including bank transactions) and the power agent cannot be traced. The suit has been filed against 10 plot owners, while the Power agent has sold about 50 plots in the same layout with same power of Attorney.