Hi Polina1337,
welcome to the Apple (user-to-user) Community !
Re: "Unable to access Music Family subscription with Family Sharing? : .... what should I do?"
You may need to activate Apple Music features on your iPhone in Settings﹥Music.
Wondering what happens when you open the Apple Music app. Eg: error message / can not sign in ?
To use Family Sharing, you need an Apple ID
Apple support have an article online (link below) that may be helpful:
Join Apple Music on your iPhone, iPad, iPod touch, Mac, or PC - Apple Support
eg: says:
On your iPhone, iPad, iPod touch, or Android device
✽ Open the Apple Music app and tap Listen Now.
✽ In the upper-right corner, tap the photo icon.
✽ Sign in with your Apple ID and password.
Seems everyone automatically gets their own Library, to which they can add the music they choose.
How to: Listen to music and more in the Apple Music app - Apple Support
Previous purchases may be available in the "Library" in the Music app.
or
How to: Redownload music - Apple Support
and
What to do: If you can't find your family's shared content - Apple Support
________________________
If needed: Trouble-shooting:
You may need to receive an invitation (eMail) from the family organizer, and accept that. invitation.
How to: Share Apple and App Store subscriptions with family members on iPhone - Apple Support
or
The "Music Support" website has info./ support / contact (online chat / phone / email etc):
(There's a "get Support" link at the bottom of the webpage below:)
Music - Official Apple Support
All the best :-)