Passwords for Account Managers/Admins
When we reset the password for one of the email addresses associated with the master account, it changed the password for all of the other email addresses associated with the account. Are the email addresses listed under the "Manage Email Addresses" user settings just aliases for the same primary account? Or should each email address have their own separate password? Seems odd that all users would use the same password.
Upgrade Storage
You should delete the ones you've entered. Once you've done that, people can create their own Zotero accounts, and you can then invite them to groups as desired.
If you want more flexibility, consider getting a Lab account, which is a still very reasonably $450/year for 15 unlimited accounts: https://www.zotero.org/storage/institutions