Rights of person to transfer immovable and movable property.

There's no illegality in he selling the property by executing the registered sale deed in the presence of sub registrar when he was of good mental health.

Therefore any challenge to the sale deed may not be maintainable.

Adopted son has no right to question the sale of his adoptive father, he only gets right in ancsetral property of his share only, adoptive father alone cannot adopt without consent of wife when he has daughter. Adoption becomes invalid.

The property would have been passed down based on the Hindu Succession Act of 1956, the Special Marriage Act of 1954 or the Guardian and Ward Act of 1890. 

If the daughter can establish that the property transfer was done when her father was in a state of sound mind or had the right mind state to be able to make a decision of property transfer then any other objection to it cannot be maintainable.

The adopted son cannot create any legal issues unless his share of the property has been tampered with. 

There should be no issues for the purchasers of the property if it is established that the property has been legally obtained by his daughter and the adopted son has got his share of the same. Selling the property which is owned by the daughter will not create any legal issues since the property belongs to the daughter and doing anything with it is her personal choice.

Admittedly, the property has been transferred to the daughter through a duly registered deed. the transaction is valid unless proved otherwise. The onus of proving the transaction to be invalid vests with the person who makes such an averment. It could also be that the challenge is beyond the period of limitation.