Does the partition suite sustains?

My father bought a land with unregistered sale with possession document from 2 owners in 1989 and 1999. The division of the land in two halves has happened before our purchase in 1989 but through unregistered affidavits between their fathers. His plan is to obtain decree from the court that no partition has happened and so the sale is not legal. Their fathers are not a live now. Now one of the owner is demanding money to accept the sale and the other owner is accepting that the sale had happened long back when his father is alive. Now that cunning owner has approached court with the partition suite claiming for his share from the other owner saying both are equally enjoying the rights and possession. They even doesn't have any documents regarding the land but we have link documents as we have taken the possession of the land from the sale date and we paid the total amount of consideration and taken immediate possession of the land. we are actually in possession of the land doing cultivation and constructed a shed to keep our belongings. The shed has been taxed by local municipality and power and water connection we have in our name.