Apple one subscription

Indeed it could. I didn't mention this because it sounded like you could see them as family members, just that they couldn't get access to Apple Music.

Legal - Apple Media Services - Apple

"All Family members must share the same Home Country."

Share purchases with others in your Family Sharing group

https://support.apple.com/guide/mac-help/share-purchases-with-your-family-mchlc2b37692/mac

"To share purchases, family members must be in the same iTunes Store country or region."

Sometimes it helps to have the devices involved take a fresh look at settings:

- Try signing out of accounts and back in again.

- Restarting is a simple step that can resolve many unexpected behaviors.

If a problem persists, particularly over several days, try contacting Apple for assistance:

Click here --> Choose your country or region - Official Apple Support Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.

or:

"See a list of Apple phone numbers around the world."

Click here --> Contact Apple for support and service - Apple Support