michael.mariart on "Install Duplicate WP site on a Sub-directory"

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1. Backup files and folders
2. Backup database
3. Add files to new sub-domain
4. Create new database
5. Import SQL file to new database
6. Change DB connection settings in wp-config.php
7. Run search & replace tool
8. Log in as admin to change administrator accounts
9. Edit any files that require it

As you've said, yes the admin username and passwords will copy over as well, but that's expected when you do a copy like that. You need to log into each one and add/edit the admin user to be whatever you want that account to be for each site.