How to divide pension and gratuity between two wives

Sir. My father had two marriages. First wife had 2 sons and one daughter.. one daughter and one son is married. First wife has been died. Then my father married to another girl.. I m the son of second wife. We are three brothers. My father was a govt employee. Now he is no more. . Now the problem is arised about division of PF and other funds which will come.. There is a letter came from govt about Gratuty .. which came by mentioning the name of my mother who is second wife.. now the sons and daughter of first wife saying that they want half share in the amount of gratuity.. Are they should get half shre or not.. and one thing.. there is no nominees.. plzz reply me fast