I am surprised that journalists are just satiisfied with quoting "experts" concerning ethics and in this case, nepotism. The Statutes make it clear that The President (Title 5 article 3110: (2) “public official” means an officer (including the President and a Member of Congress), a member of the uniformed service, an employee and any other individual...) cannot employ a member of his "relatives" (relatives as defined in statute Tittle 5 article 3110 :(3) “relative” means, with respect to a public official, an individual who is related to the public official as father, mother, son, daughter, brother, sister, uncle, aunt, first cousin, nephew, niece, husband, wife, father-in-law, mother-in-law, son-in-law, ...)
The way around this for lawyers is to not pay the relative. Yet, if he is not payed, he is not an employee, if he is not an employee,  he should not get access to high security knowledge because he is not bound by contract. Further, as a son-in-law, all other ehics title apply.