agreement to sale made on 5rs stamp in 1984 which was not registerd.

My Father made a agreement to sale of 3R land in 1984 from a Mr Raja and Brothers on 5Rs stamp paper with consideration sum of 20K out of which 10k was given in cash during the execution of the agreement, with the condition that the rest money will be given once they have the execute the sale deed . The agreement to sale was executed in front of witness along with brothers which as not registered as it was trusted deal between the party and my father. At the time of execution of agreement to sale the land for which agreement was done Mr Raja & brother had their name in ittar hakka and a litigation case was in progress in court for the same land (Kulkayad case) for which they needed money. The possession of the said land as per the agreement to sale was taken and my father build a house on the land along with garden area. and has been paying the property tax for the Structure since possession of the land. there was no hindrance/notice/objection by Mr. Raja & brother till now 2017. In 2018 Mr. Raja & brothers now wont he case and have their name 7/12 extract. In 2022 Mr. Raja & brother tried by manhandling and getting machinery to destruct the house with the any permission to vacatethe land . Now as per the agreement to sale they have to execute the sale deed , which they are now denying and asking a vacate the land . They are now trying to show case my father as a tenant of the land by making some false documents and then forcing with the law to vacate the land and destruct the house. Question What can i do in such case ? would the agreement to sale be Valid if this they file a case in court showing as a tenant ? What are other ways i can have this sale deed executed, as we are showing interest to execute the sale deed with 10 times increase in the remaining sum amount.