Fraud on part of the vendor

My father and my mother had jointly purchased a property along with a residential property vide a duly registered deed of sale in 1995. For all these years we had rented the said premises. Now after the death of my father in Nov 2016, in February 2018, we have got a court summons that a case has been registered against us for fraud. It is alleged that the signatures of the vendor and his wife were fraudulently taken by my father under the pretext that they were being taken for a leave and license agreement.He has claimed that we were staying at the said house on leave and license basis and were paying the rent regularly until August 2016, which is absolutely false. The vendors also deny that they got the consideration as written in the sale deed. They rely on the record of rights, which we did not mutate for the last 22 years. The complainant has filed a police complaint of fraud against us and asked for the possession of the said plot and house. The vendors have neither attached any rent receipt nor any leave and license agreement copy with the complaint under specific relief act. Can I file any counterclaim and seek compensation for this false complaint under any act or for defamation? is there any quantum as to how much I can claim? Any other complaint required from the criminal side?