• Help on adverse possession and Section 16(3) in Bihar Land Reforms Act

Dear Sir, 
Kindly help on the matter as under: 
1) I have a ancestral land where my home is situated. Piece of the land partially on our super grandfather name and partially on the land belonged to neighbor(Disputed land) lets say A Great grandfather who is residing two houses away from us. We are residing on the disputed land from last 3 generation. However there is no documents with us which was agreed between our great grandfather and our neighbor ancestor. Although they have agreed that we should be living on this land for many decades. We have build our residential house over-there. For last many years. 
2) Recently Mr. A has sold the that parcel of land to another our neighbor who is very hostile in the nature and acquiring nearby area very aggressively. We have offered to pay the price to the A but our hostile neighbor has paid higher price and entered into the registered agreement with them 2 days ago.
Our objective: 
1) To stop the mutation of the land as physical possession of the land is with us for many decades and there was no objection from the family of the original land owner. 
2) Can we file case against the seller of the land because we have build our house and objection were raised for many decades then they sold it to other person just to harass and blackmail us. 
3) Can we file case against the Registered of the land as we should be first person to purchase the land based on our uses, even we are ready to pay the amount of the agreement on which land is sold to other party. 
4) The person who bought the land is having many land purchased and many land is not able to get mutation because of their hostile nature of acquisition. Can we leverage these records in our favor in the court for above objective. 
5) Any other solution you may please provide with relevant section to stop the Mutation, challenge the registry of the land, and taking adverse possession based on above facts. 

Expecting point wise reply.