Capital gains

A parcel of land with 3 shops situated in a rural village under Gram Panchayat and belonging to my deceased maternal grandfather was purchased by him in the early 1970s. Now my two maternal uncles are planning to sell this off for Rs. 21 lakhs. My deceased mother's share is 1/3rd, i.e., Rs. 9 lakhs. Please advice whether this attracts Capital Gains Tax and if so, the quantum of such tax.