In my Outlook Calendar there are about 12 "group" calendars listed w/ people's names I do not know, and never gave permission to view or share calendars. I am not able to remove them.

Those group calendars are most likely calendars that have been shared with the account or added automatically, not people who can see the personal calendar. To address this, there are two separate tasks:

1. Stop sharing the calendar with others (if it is shared)
2. Remove shared calendars from the own view

For Outlook on the web (Outlook.com):

1. Stop sharing the calendar with someone
   1. Open Outlook on the web and go to Calendar.
   2. At the top of the page, select Share, and choose the calendar to manage (by default it is named Calendar).
   3. In the list of people with access, select any name that should no longer have access and choose Remove.
   4. This removes their permissions. If they are inside the same organization, the calendar is removed from their list; if they are outside, their copy stops syncing and no longer receives updates.
2. Remove shared calendars from the own list (mobile scenario)

If these calendars are appearing in Outlook for iOS or Android and are just cluttering the list (not a permissions issue):

1. Open the Outlook app and go to Calendar.
2. From the list of calendars, select the gear icon next to the shared calendar that should be removed.
3. At the bottom of the screen, choose Remove Shared Calendar.

This only removes the calendar from the own view; it does not affect any permissions on the other person’s calendar.

If the calendars still cannot be removed or do not appear under Share in Outlook on the web, contact the mail provider or Microsoft support with screenshots so they can check for any account or directory issues.

References:

• Share your calendar in Outlook on the web
• How do I remove someone from my list of shared calendars?