Hi x-teacher,
Welcome to the Apple Community.
Re: Is there a way to eliminate user B and it's iDrive and get everyone on the same page?
Sorry I'm not an expert on this ... however no experts have yet seen your post, or have not seen fit to reply.
Expert help may yet be added ... we are all Apple users, like yourself, volunteering to help troubleshoot.
If needed for safe-keeping: Download (or Move to Mac) User B's iCloud Drive files
so you can delete files and free up space in iCloud
How to: Upload and download files from iCloud Drive on iCloud.com – Apple Support (AU)
and how to: Work with folders and files in iCloud Drive – Apple Support (AU)
Access and manage your files in iCloud Drive - Apple Support
Seems you could then turn off iCloud Drive for Mac User B, and the iPhone, and iPad.
Sign out of iCloud on your iPhone, iPad, iPod touch, Apple TV, or Mac - Apple Support
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You might want to back-up user B's files on Mac eg: to a zip-drive), or move / copy them to where User A can access them.
It would be good to delete all Users B's files taking up space on your Mac, if you will remove access to them.
One way to eliminate User B:
On Mac: Click the Apple icon on the left in the top menu bar.
Choose System Preferences from the drop-down menu that appears.
Click the "Users and Groups" icon in the System Preferences window that opens (grey, with two black figures icon)
Click the padlock at bottom left in the Users and Groups window.
Enter the password you use on your Mac in the box that appears
Now you can Click on User B to highlight it,
and eliminate user B by clicking the minus sign ( see + and - at bottom left / left (white) column)
Click the padlock to safeguard again
As your Mac, iPhone and iPhone all use the same Apple ID:
and as User B no longer exists,
You may want to turn iCloud Drive access back on, for the iPhone and iPad
Apple support have articles online (links below) that may help:
Set up iCloud Drive on all of your devices – Apple Support (AU)
Access iCloud Drive files from your iPhone and other devices - Apple Support
If needed:
There's a "Get Support" Link at the bottom of the iCloud Support Team's website:
iCloud - Official Apple Support
Hope this helps :-)