1. If your father purchased that property by a  registered sale deed then it becomes his own and absolute property. 

If some other person is also claiming the property on the basis of the sale deed in his possession,  then your father may file a suit for declaration to declare the title to his name on the basis of his registered sale deed and possession and enjoyment of the property till date. 

2. You may have to adopt due process of law as suggested above. 

3. If the opposite party is pressurizing or prevents you from selling the property you can approach police for protection. 

It appears land has been fraudulently sold by A to B and your father 

if B has prior registered sale deed in his favour he would have marketable title to property 

3) you should return money to C and cancel sale deed by mutual consent 

4) settle with B 

5) sue the seller A to recover money paid by your father with interest 

Lawyer can draft deed of cancellation of sale deed 

it should be duly stamped and registered 

You can settle with person B. Or file FIr against A for fraud. If you name is on mutation and registration documents you don't have to worry

If the sale deed was registered within3 years from now then both the purchaser and the seller have to execute the registered cancellation deed before the concerned registrar office.

- If your father had purchased that land by way or registered deed, then legally he is the owner of the property , then the sell by Person A is invalid .

- If no title deed in favour of your father was executed by person A , then he was having his right to sell that land after informing your father to person B. 

- Further , if that land was in the name of person B , then how A can sell that land to your father , and then the person B is having right to claim that land from your father . 

- Your father can lodge a complaint against the person A for the offence of cheating and under other provisions. 

Title is important for immovable property. The absolute owner of the property has only to transfer his rights to any person .First check the sale deed executed by A in favour of your father. If possible check the deed executed to B also . 

It is understood that  the possession of the property and B's claim contradicts. Please check the encumbrance certificate and get a copy of the same from registrar office. Encumbrance means the charges or liabilities created on a particular property, whereby it is held as a security for any debt of its owner which has not been discharged as on date. An Encumbrance Certificate denotes the charges in the ownership or liabilities created on a property that is held against a home loan as security. This document consists of all the registered transactions pertaining to the property for a particular period/sought period. The certificate that is sought for a particular period evidences the property purchase/sale, or the presence of any transaction or mortgage for that particular period.

Without perusing the documents it is difficult to give a correct answer with regard to the rights in the property.

A registered deed can cancel any time by the mutual consent of the parties by way of executing a cancellation deed. 

Dear sir,

if your father has a register sale deed in his name , then he can declare his title. If the opposite party is still coercing you from selling off the property then you can seek police protection

Thank you

Your father is liable to pay C as he does not have clear and marketable title to property 

A has fraudulently sold land to your father when he had already sold to B 

If person C is demanding the money from you on the basis of the objections by person B, then he should not have sold the land to person D.

If you want to cancel the sale deed in favor of C, first C has to execute a registered cancellation of sale Deed between him and D, jointly along with D.

After that you can jointly execute a registered cancellation deed along with C to cancel the sale deed executed in favor of C. 

After this step your father can file a suit for title declaration against B

If C sold that  land to D then why did he ask money from you ? If your father had full rights over the land how you should  sold that land to C .

If B is only obstructing without proving his right or filing a case against you or your father then how A LIABILITY AROUSED TO PAY

- Since that land was sold to person B by A , then B can claim the property. 

Whoever  has suffered has cause of action to file the same