Ancestral property Land sold by grandma (paternal ) -Reg

My ancestral property being a plot of land at Village Endiyur bearing survey no., 124.12.023,[Document No. 1605 of 1955] measuring about 46 cents was jointly owned by my late grandfather Mr.Mari Gounder and late grandmother Smt. Viruthambal (paternal). And my late grandmother illegally and unauthorisedly sold without my knowledge and permission not only her share (50%) but also my equal share in the land during the year Oct.1993 to one E.Kuppammal,(1st wife) W/o. Mr. S.M. Elumalai APP advocate who by virtue of his influential position as an advocate in the village bought the said plot of land coercively and got the same registered in his second wife’s name E.Banumathi, W/o. Mr. S.M. Elumalai APP advocate which land grabbing took place in the year Oct.1996 respectively. When the plot of land was sold by my late grandmother, I was too small to understand the land deal, was doing diploma (DME) moved to Chennai for my higher studies and then took up the govt. job in which I still continue and got settled down nearby office in Chennai suburb. I inherit the balance 50% of the land through my father (who died in the year 1973), who in turn inherited the same from my grandfather Mr. Mari Gounder. On checking the records and the antecedents, I have now come to realise that I am entitled to 50% share in the plot measuring approx. 23 cents which was illegally sold by my grandmother Smt. Viruthambal (who was not my natural guardian then to legalise the sale under any circumstances whatsoever) to one Mr. S.M.Elumalai through hoax and coercion without my knowledge and written permission which transaction is absolutely illegal and ipso facto void ab initio In view of above, Please tell me the legal opinion, how to get my ancestral property. Regards J.Jaganathan