Hey dabo256,
Thank you for using the Apple Support Communities! We understand you have questions about subscriptions and Family Sharing. Let's help.
To start, there can only be one Organizer per Family Sharing group, that heads all purchases and subscriptions to share. That means, either you (Member A) have to set up the Family Sharing group to be the Organizer and members B and C join your group. Or, member C remains the Organizer of the Family Sharing group where both members A and B joined, and member C signs up for the Apple One Family or Premier subscription to share it with you both.
You referenced If you subscribe to Apple One and use a different Apple ID for iCloud. Do either you (member A) or member C use two different Apple ID's on your personal devices; one for iCloud, one for the iTunes & App Store? Or, do you only have one set up per device/user?
These articles may also be helpful:
What happens to your iCloud storage when you sign up for Apple One - Apple Support
Bundle Apple subscriptions with Apple One - Apple Support "If you already subscribe to Apple Music, Apple News+, Apple Arcade, or Apple TV+, you don't need to cancel those subscriptions. They will automatically be canceled when you're billed for Apple One."
Leave Family Sharing - Apple Support
Add or remove members from your Family Sharing group on iPhone - Apple Support
Let us know if you have any further questions after reviewing this reply and the given resources.
Best regards.