Shareable subscriptions are available to members of a Family Sharing group, that each have an Apple ID account.
Subscriptions that were started in the Apple TV app can be watched in the Apple TV app on other devices, not in the content provider app, and not on the web. It works automatically through the grouped Apple ID accounts without signing in for each service. Then each group member can access the service on their own account (no account credentials shared).
Subscribe to Apple TV channels in the Apple TV app - Apple Support
About Family Sharing - Apple
Learn what you can do with Family Sharing - Apple Support
Set up Family Sharing - Apple Support
Family Sharing has to be set up by one adult from the group on their iPhone, iPad, or Mac. That doesn’t have to be the same person as the subscriber.
Add a family member to your subscriptions from Apple - Apple Support
