Ask them who paid you Rs.20 lakhs whether they have paid capital gains tax or not?
You should know as to what was the sale price. What is your share. If what you got i.e. Rs. 20 lakhs is exactly your share from the sale proceeds (i.e. if 100 lakhs is the sale consideration and you have 1/5th share and got Rs. 20 lakhs) it means no Capital Gains has been paid.
Then you have to pay. Capital Gains tax is 20% of the capital gains.
Without knowing this, you have gone to the conclusion that "there is no tax for inherited money".