Is it permissible to receive a father's pension due to suffering from a mental illness?

If the father is alive, it is impermissible to take from his money except for the amount of obligatory maintenance if the son is unable to earn a living. If the father is deceased, the pension is either deducted from his salary, in which case it is a right of the heirs. Or it is a grant from the state, in which case it is permissible to take from it if the required conditions for entitlement are met.