Asset without patta

Hi All, Greetings for the day, I would like to understand the process how to get Patta for unregistered land, detailed information as below. 1. The property was bought on 90's in writing but the document was not registered legally. 2. Property owners has passed way and her sons are living in the same place. 3. The asset was belong to 3 children and very elder son expired very recently. 4. Now the other family members were trying to get Patta for the property but finding it difficult. Would appreciate if someone could help me with process in details along with action. Let's me know if any questions. Thanks 😊