3.—(1) For the purposes of this Order a person is a member of another's family if—
(a)he is the spouse[F1 or civil partner] of that person, or he and that person live together as husband and wife[F1 or as if they were civil partners], or
(b)he is that person's parent, grandparent, child, grandchild, brother or sister.
(2) For the purpose of paragraph (1)(b)—
(a)a relationship by marriage[F1 or civil partnership] shall be treated as a relationship by blood,
(b)a relationship of the half-blood shall be treated as a relationship of the whole blood, and
(c)the stepchild of a person shall be treated as his child.