Property Under Gramakantam

I'm looking to purchase a property which comes under Gramakantam. The below is the history of the property. 1. There is a document of approval/permission issued by the Sarpanch of Gram Panchayat show the person X as the owner of the said property. 2. In 2003, person X transferred the property to 3 sons (namely 1, 2 & 3) through registered gift deeds. 3. On all 3 gift deeds the house number is same as it was just land when it was gifted. 3. In 2006, son 2, the owner of a portion has applied for the building construction and has approval letter and plan of construction approved by Municipal Authority. 4. In 2010, son 2 constructed a house on his portion of the property. Same was done by other sons. 5. In 2018, son 2 wants to sell his house. But property tax is still paid for one house number and the name shown on the property is Son 1. Is it because son 2 & 3 has not done the mutation of his portion of the property. Can son 2 apply for mutation now to change his name on the property tax for his portion of the property ( land & building) 6. As a prospective buyer what all the documents I need to ask the seller to make this transaction a legal one and to avoid any legal issues in future.