Capital Gain

My father sold property worth Rs. 40 lakhs in August 2019. 

In March, 2020 he deposited all of that money into a Capital Gain account in the same bank as we were unable to buy another during that financial year.

Now in December 2020, he died due to illness.

Now we want to use that money to buy another property.

Do we have to Pay the Capital gain first to use that money or it's still Tax free ?

Also the Bank insisting on giving the money only to the nominee (which is me) whereas I want my mother to be his Legal Heir and want to buy the property on her name.

Also the Income Tax department demanding a Legal Heir certificate first before signing the FORM-H and authorising to use that money.

So kindly guide us on this matter.