How do I go back in to share iCloud with another family member
How do I go back and add another family member to my iCloud plan
Are you the Organizer? If yes, invite hte person. Click on this link to learn how to set up Family Sharing --> Set up Family Sharing - Apple Support
Read the section: "Invite people to join your family"
If not, when you share the subscription with one Family member you will share with all.
Add a family member to your shared subscriptions - Apple Support