What is the ruling on eating and drinking from stolen utensils, and are the children sinful for that if they advised their thieving father and he did not respond?

It is not permissible to take a Muslim's property without their consent, especially from relatives. The sanctity of a relative's property is even greater because it involves the rights of kinship and familial ties. Your father's taking of the utensils in exchange for a service for which he was not compensated is not sufficient to justify his action. This is because he might have performed the service without an agreement on wages. Even if his right were established, how can he guarantee that he only took what was equivalent to his right without exceeding it? Therefore, do not use these utensils, and gently and cautiously advise your father to seek what is lawful and to beware of consuming others' property unlawfully.