Legal Advice Needed Regarding Land Ownership Dispute

I am reaching out to seek legal advice regarding a land ownership dispute that my family is currently facing. In 1981, my elder paternal uncle purchased a piece of land in the name of my younger paternal uncle, using a INR 5 rupees stamp paper. However, it was ideally meant to be purchased in the name of all three brothers. Unfortunately, the land was not registered at the Tahsil office. Instead, there is only a pencil entry on the Grampanchayat's 7/12 record. My elder uncle passed away in June 1998. Subsequently, the grandson of the original seller coerced my uncle into signing a gift deed transferring the property to him. The original seller passed away in 2004. Currently, the grandson is harassing us and demanding a large sum of money. We want to resolve this issue and ensure that the land is registered in the names of all three brothers. Could you please advise us on the legal steps we can take to rectify this situation and secure ownership of the land rightfully? Thank you for your attention to this matter. I look forward to hearing from you soon.