Go to System Preferences > Users & Groups and select Password. The other accounts may still be listed. If so, click the lock icon and enter your password. Then, select the accounts that you want to remove and click - Hopefully, that will do the trick.
OS 10.15.3, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365