Property Transfer

My mother purchase a property in a village out of lal dora in 2000, During purchase, a will, Sale agreement, GPA, SPA, Affidavit and Byana done. No documents was registered. In 2002, the seller got expired, In 2005 his son has approached us that he will get the property transferred or registered in my mother name and taken the original documents with us, but returned only GPA, SPA and Affidavit. We have forged a complaint against him in police station also. Now we have photocopy of Will, Original Byana copy, Original GPA, SPA (no documents registered). In 2007, the son of seller filled the court case for possession of house, however the case got dismissed as he did not appear in the court later on and he went to Australia. Now, as per intakal Property is transferred to his legal heirs(two daughters and two sons). Now We have possession of house from 2000 till now. Now we want to transfer the property to our name, but we have not original will copy. Please provide the correct advice as every lawyer is giving different advice. Also please confirm is there any law for property transfer if we have 20 years of possession.