How to calculate capital gains tax on property sold at less than stamp value

We have sold our ancestral house in May 2017 for Rs 36 lakh after the deed was duly registered. The amount was shared among our three brothers and a sister and each received Rs 9 lakh. As per the registry office, the present market price of the property (land & building) is Rs 44.21 lakh. What will be the capital gain tax liability? The property was purchased in 1967 at a price of Rs 6000 by our parents. Later, some rooms were constructed in the landed property but we do not have any proof of those expenditures. We are regular, retired tax payers. Should we invest the entire sale proceeds in NHAI/REC Bonds? One of my brothers (who has no property in his name) invests the amount to purchase a flat. 
The property was purchased constructed by your parents prior to 01.04.2001. The cost of acquisition of the property shall be the fair market value of the property as on 01.04.2001. You will have to obtain a Valuation Report from a government-approved valuer  .. 
As the sale consideration of Rs 36 lakhs is less than the stamp duty valuation of Rs 44.21 lakhs, as per the provisions of Section 50C, the stamp duty valuation shall be deemed to be the sale consideration of the property. 

As the property is held for more than 2 years, you will be eligible to claim the benefit of indexation. The net long-term capital gains i.e. stamp duty valuation less the indexed cost of acquisition shall be equally divided among the 4 of you and in the hands of of each individual it will be taxable as long-term capital gains. 

Each individual can claim the deduction us. 5454EC subject to satisfaction of the conditions of respective section.