Sale agreement made based on notarised GPA in Karnataka

Hi, I had purchased a property from Mr A in 2006 by sale deed. Later I came to know the property was under litigation between Mr A and B. After lot of pressure put by me on Mr A, Mr A agreed to provide me a alternate property. He provided me a alternate property in 2010, I have constructed a house on it and living since 2014. I have also been requesting Mr A to cancel the sale deed which he had made to me on the disputed property. However, he refused and he asked me to provide a GPA of this litigated property to one of his agents. I refused to provide an registered GPA as I did not want to get into any legal trouble and insisted on a cancellation deed. However he put lot of pressure on me and forced me to provide a notarised GPA in the name of Mr A's agent (Mr C) in 2016. Since then MR C has filed a case on my behalf over Mr B, on the disputed property and also constructed a house on the disputed property (in my name) without my knowledge. I received a notice from the court and later I came to know of the case proceedings. I approached Mr A on this issue and again requested for a cancellation deed. He refuses saying his case will become week and he wants me to execute a sale deed of the disputed property on the name of Mr C and promised he will not involve me in the case henceforth. Note: there is no stay so far on the case. I cant believe either Mr A or C as they may later file a case on me based on the sale deed if he looses in court the disputed property. Mr A and C are also threatening me that they will execute a sale deed to Mr D (another agent) based on the notarised GPA and file a case against me!! They are forcing me to register the property to Mr C. Please advice what to do.