Risky and not worth it, in my opinion.

With immediate family, with the same surname, travelling on the same flight, problems are unlikely. Even if you were unlucky and got a pedantic lounge receptionist, the worst outcome is likely to be a polite refusal or direction toward the J lounge.

That situation is very different from a staff member soliciting to be guested in by a stranger, probably on a different flight. Without clear connections between host and guest, there is a greater risk of arousing suspicion in the first place. Real potential for uncomfortable questioning, refusal of the guest, embarrassment for both parties, and risk of disciplinary action for the staff member if found to deliberately abuse the policy.