Procedure for tax on a property received by sale deed

My Father(Hindu) Got a notice from Income tax Department on sale deed executed in 16-17 whose value is 1 crore 45 lacks. Actually that property was my father's ancestral property on his uncle's name. His uncle gave this property on sale deed instead of gift deed, as there were no transaction on amount. Now income tax is asking about the transaction, Business details, all purchase/ sale in that session, Bank account details, tax paid or not , ITR filed or not etc. After getting ownership of that property, my father sold that property to some people due to financial issue. My father was not aware about ITR filling next year. Now we are totally confuse what to do? Please Give some Suggestions.