Hi there, based on your description and all attempts, I can tell the Toshiba drive's not showing up happens due to the cable that you use. Generally speaking, some simple cable or adapter has no ability to run an external hard drive because it comes with no power supply. Therefore, a USB hub with multiple ports is perfect for you provided that you need to connect so many hard drives to different devices.
Hope this answer helps you solve the Toshiba external hard drive not showing up on your Mac trouble. Take care~