Relinquishment deed

If the widow inherited the property from her deceased husband who is reported to have died intestate,  then she will be termed as an absolute owner insofar as her inherited share in the property. 

It is not relinquishment but it will be transferred by executing a registered sale deed. 

The signature of her children or grandchildren is not required. 

I opine that according to the Hindu Succession Act, the Class-I heir of the deceased includes his widow, children and mother and hence the relinquishment deed shall be executed/signed by his legal heirs for his share.  But you(the legal heirs of your father) cannot relinquish your rights for the loan purposes but can execute a sale in favour of a Mortgage(loan) deed in favour of another person by paying necessary stamp duty and registration fees.