SELECT
cd.id AS `Client ID`,
CONCAT(cd.firstname,' ',cd.lastname) AS `Client`,
ca.email AS `Client Email`
FROM hb_client_details cd
JOIN hb_client_access ca ON (ca.id=cd.id)
INNER JOIN (
 SELECT firstname, lastname FROM hb_client_details GROUP BY firstname,lastname HAVING COUNT(id)>1
) dup ON (dup.firstname=cd.firstname AND dup.lastname=cd.lastname)
ORDER BY cd.firstname,cd.lastname ASC