Is it permissible for an employed heir to take from the one-third of the deceased's wealth bequeathed to the poor and needy among his heirs, knowing that the deceased bequeathed two-thirds of his wealth to the Haram?

A will bequeathing more than one-third of the estate is not permissible, nor is a will in favor of an heir, unless the other heirs consent. Your grandfather's bequest to the Haram (Sanctuary) is enforceable only up to one-third [of the estate]. Any amount exceeding that, or a bequest to poor heirs, is not enforceable unless the heirs approve it. If some heirs approve the will, it is only enforceable with respect to their share. You are permitted to take from your grandfather's bequest if you are poor and in need. A poor person is one whose income is insufficient to cover their essential needs.