Property dispute

Sir/Madam, 1. I have purchased an open plot (Dec.2012). 2. Seller (70 years) taken total consideration and registered in my name. 3. Seller said this property belongs to his ancestral property and singed his family (sons and daughters) members in sale deed. 4. Now his sister (72 years) filed a civil case In the Court of The Senior Civil Judge (June.13) that claiming part of ownership, partition of the property. I understand seller himself doing all this for additional money and enquired about him that is his character of cheating. Please help me, how precede this case Ar