Please help me in this regard as the amount was of my father and it should be transferred to his son n daughter rather than my uncle.
Your father made your grandmother as nominee for gratuity and other terminal benefits, accordingly she acquired all the amount and now this amount becomes her own which she can transact with at her own will and wish.
If your uncle is cheating her then you must prevail on her to not to give him any money.
You cannot legally prevent him from taking money from his mother.
The amount that was given as terminal benefits to your father was in your grandmother;s name hence it is her own in which neither you nor anyone can stake a claim or share out of it.