First of all, visit your local Revenue office & find out all details of your property.As it is ancestral property, find out your grandfather's name. With stroke of luck, they may be having it. Ask for a copy of khatiya/record-of-rights.
After you have followed previous step, visit Tehsildar/SDM's office & inspect land records. All land details can be obtained from the khatiyan. If your land records are available from an old date, start searching the LR from that date itself. Cross-check every detail from public documents such as tax register, heirship cases register & the like, as these documents would cover deceased landowner's name & his heirs who are your ancestors.
Once you get material particulars (e.g. survey no/sheet no/Khasra no/Halka no/village etc) file an RTI application to your Revenue office's PIO, asking for whatever particulars/information you seek u/Section 6 of the RTI Act. These would include certified copies of record of rights (khatauni), field-book, mutation register & village map, amongst other particulars. Pay whatever is the application fee.
Should you have any queries, please feel to revert at basu_kunal@hotmail.com.I will be more than happy to advise you.
Regards
Advocate Kaybee