If the person who seeks to repay the loan, can give an affidavit to the effect that he had taken a loan without interest from your late father who was his friend, then that may help.
Obviously accepting a bank transfer is not going to be without legal problems
I take it that since the loan transaction is a very old one for which there is no documentary proof and the loan may also possibly be given by cash, then the question would arise about the known sources of income of your father for lending an amount of 35 lacs and whether this money was declared in his IT returns as an asset.
So if you are accepting the repayment by bank transfer , your case may get selected for scrutiny by the assessing officer and you would have to explain everything
At the highest you will have to pay tax on the amount that is being repaid to you
It's much better and advisable to receive the money by proper banking channels than in cash since repayment of money in cash will bring both the borrower and the heir of the lender in legal trouble since under the IT act no borrower is permitted to repay any loan in cash and also receiving cash in excess of 2 lacs is prohibited
So please consult a proper CA