"no, the paye credit is not available in any case where a family member of a director is employed in the company"
that's not true,
you are correct with the spouse but not with the children.
the credit may be claimed by children of proprietary directors and the self employed who are full time employees in the business of their parents and where certain conditions are met, which are -
(a) PAYE must be operated in respect of the employment, and
(b) the individual's income from the employment must be at least €4,571