Hi @Dzyyy thansk for posting to community!
Sounds like your brother may be upgraded through a third-party vendor like Google Play or Apple. At this time it's not currently possible to join or upgrade to a Family Plan from these vendors. Because he has to wait for his subscription to end, unfortunately, this will remove is offline content and he will have to redownload the content when he joins your family plan. (Sorry about that!)
We do have a feature request to restore offline downloads after reinstalling or resubscribing. If this is something you'd like to see on Pandora, I would recommend upvoting this idea - this helps us know which features our listeners are wanting to see.
Hope this helped to asnwer your question.
