Re-convey of property

Hi Kaanoon Team, Greetings. My grandfather performed a conditional sale of ancestral property in year 1962 and registered the property in the name of Vendee. Condition was that if my grandfather intends, he could buy back the property at selling price, within 3 years from date of the conditional sale. Though my grandfather paid the complete amount to the Vendee's representative within 6 months from date of conditional sale and obtained a receipt acknowledging the full and final amount is received for re-purchase of the property and that the Vendee would render required help to register the property in the name of my grandfather. The Vendee's representative handed over the conditional sale deed (original) to my grandfather. The Vendee has evaded re-conveying the property to my grandfather stating lame excuses and that we could continue to enjoy the property since the full and final amount has been paid and that he would have no claim on it. My grandfather, the Vendee and the Vendee's representative are no more. We are in continued possession of the property even after the conditional sale since my grandfather entered into a rental agreement with the Vendee to continue to reside in the property as a tenant. No rent was demanded or paid to date. We are paying property tax and utility bills for the property as prior to the conditional sale. Request to know how we could have the property registered back to us. Vendee's name figures in the EC. Appreciate advise please. Thanks and Best Regards