This need to assess the competence of parents where there is a difficulty that some are personality disordered and dissembling is why it's better to focus on the potentially alienated child's symptoms. Dr Childress has provided a set of diagnostic criteria that can be used to make an unambiguous assessment of whether a child has been alienated by a narcissistic or borderline parent (and so is being more generally abused) http://drcraigchildressblog.com/2014/06/18/diagnosis/

This could break the 30 year court failure to act on Gardner's PAS model.