When I had primes he was on it but I just found out Once the Prime Ended ALL of the apps Vanish from his PC

Not sure what Prime had to do with him being on the accounts. What he needs on his PC is Music, Movies & Audible Mgr
I looked under Audible which said I could add him IF he had his own account

or as a child IF I Pay the FreeTime fees

But I don't see any other ways.

in advance