Capital gain problem back date case.

After the death of a father 2 years back, Two sons mutually agreed & signed a legal deed, and divided and took an equal share of a residential house which was purchased by their father around 40 years back. They don't have any land papers �and even dont know the amount paid at the time of purchase of land by their father.�There was no HUF created. Both sons are regular tax payers but they havent done any tax treatment or entries till now. Q1: Was any tax treatment to be done at the time of taking that property by the sons? Q2: If q1 is affirmative, �Since it is a back date case, what is to be done now? Q3: Now one of the brother want to sell the property to a person, and want consideration in white,? So how can he do that coz he hadnt done any entry etc when he took his partition?