What is the ruling of Islamic law regarding demanding repayment of a loan after the death of the lender, when the debtor claims that the deceased forgave him, and her brother and his wife bear witness to this?

If the deceased sister's brother claims that she absolved him of a debt, and the heirs do not believe him, he is required to provide evidence, which is the testimony of two men, or one man and two women. It is also permissible with one witness and the claimant's oath. The testimony of a wife for her husband is not valid according to the majority of scholars, while the testimony of a brother for his brother is permissible according to the majority of scholars. So, if the deceased sister's brother testifies that she absolved her debtor brother, and then this debtor takes an oath, his liability is cleared.