Leaving a family
Admins, members and viewers can leave a family from the family's settings or member menu. You'll lose access, and what you shared stays with the family. You can re-join later if someone invites you again.
If you're the owner
The owner can't leave a family that has other members. First, transfer ownership to someone else:
Web: Settings > Account > Family ownership.
iPhone and Android: open the family's member list, tap the person, and choose to make them the owner.
Once someone else is the owner, you can leave or delete your account.