How to add family members

See how to invite people by reading this link -->

Set up Family Sharing - https://support.apple.com/HT201088 -

"Invite people to join your family

After you send the invitation, you can check its status under the person's name in Settings > iCloud > Family on your iOS device. On your Mac, go to Apple menu > System Preferences, click iCloud, and select Manage Family. Then select that person's name to see the status of the invitation.

If you need to resend the invitation, select Resend Invitation."