Is it permissible for the father to withhold his children's entitlements from their deceased mother's pension, and do the children have the right to claim them?

If the money is your mother's property, then it is an inheritance and should be divided among the heirs according to their prescribed shares. If it is a grant from the government, it should be divided according to the conditions set by the granting authority. If your father withholds your right, you may gently discuss it with him or seek mediation from someone. If that does not work, there is no harm in taking the matter to court, as this is not considered disobedience. However, if no harm results to you, it is preferable not to sue him, and it is obligatory for you to continuously honor him and treat him kindly.