Dear Raj,
Remarriage of a widow doesn't extinguish her right to receive the terminal benefits arising out of her deceased former husband is the ratio decidendi set down by the higher judiciary in various case laws. You can browse the internet and find a suitable one to that of gratuity.
Regarding the claim of the surviving parents, it cannot be simply brushed aside based solely on the nomination made by the employee earlier. Certain other considerations like age of the parents, their socio-economic status, financial support from other surviving children would go into consideration before deciding the question whether they are entitled to a share in the gratuity payable to the deceased.
Therefore, it requires a judicial decision after holding an enquiry by the Controlling Authority under the PG Act,1972. Better, arrange to deposit the amount with the CA with a request for disbursement after an enquiry in this regard.