Thank you for reaching out to the Community. We moved your post from Chats to the help boards as its content fits better here.
There's nothing to worry about, since the saved music, playlists, followers and likes are stored on the account and not the plan, each account on the Duo plan will keep the content regardless of the subscription.
On another note, the Premium Student subscription is a discounted plan available in some countries for users that are currently studying at an eligible college/university. If your son wants to apply for Premium Student and is located on an available market, he can follow the process mentioned in this article.
Hope this helps. Let us know if you have any additional questions.
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