Capital gains

Since the land was bought in father's name, it is taxable proportionately As per the share of each person in the land.

Ok but they all given noc to Mr. A to hold and sale the land

If before NOC the land was not transferred to A, then Mr A will have to get succession certificate in his sole name. At that time the base Value of land will be mentioned in Succession Certificate. And court will leavy stamp duty accordingly. Then on Sale of the land, the total Capital Gain tax liability will be on A.

Thanks @ BHARAT CHANGELA