How does the paternal grandfather relate to the father in matters of inheritance and veiling?

Primary text

The grandfather is placed in the position of the father concerning veiling and inheritance in all matters, except in three specific exceptions. The exceptions are: 1) A case involving a spouse, father, and mother. 2) A case involving a spouse, father, and mother, where the mother receives one-third of the remainder when the father is present, but would receive one-third of the entire estate if the grandfather were in the father's place. 3) The inheritance share of the grandfather when present with full- or half-siblings, which is a point of difference.