(1)A person is a member of another’s family within the meaning of this Part if—
(a)he is the spouse of that person, or
(b)he is that person’s parent or child.
(2)For the purposes of subsection (1)(b)—
(a)a relationship by marriage shall be treated as a relationship by blood,
(b)the stepchild of a person shall be treated as his child, and
(c)an illegitimate child shall be treated as the legitimate child of his mother and reputed father.