Family Sharing group members can access content from this shared subscription in the Music app based on their own Apple Account, being grouped through the Family Sharing setup. They are not supposed to see the subscription mentioned outside of the Family Sharing settings, but would have access to the service through the Music app and their own account.
In the Music app, when signed in with a valid account, they should be able to stream any catalog music from Search, or their library, or the curated and featured music in the other tabs.
As you may know, sharing Apple Music (or Apple One) through Family Sharing requires the special Family tier of the subscription, as should be configured in the subscription’s settings. Do verify if that still applies.
What devices have the others tried to use to get Apple Music? Is it the same (lack of) result for all these users and all devices?
iPhone 12 mini, iOS 26
Unfortunately, any support doesn’t apply to beta software. We have no way of knowing if that plays a role here.