@PeteCC
Explain what you mean by "neither of them are booting."
1) When you enter the BIOS setup window (DELETE key on boot), and look at the boot drive order, do any EFI boot drives appear in the list? Can you set up the boot drive order in the list? If no boot drives appear, then most likely none of the drives has an EFI folder to boot from.
2) When you hold down the F12 key on boot, do any bootable drive options appear in the list. If not, then there is nothing to boot from.
3) Do any of the external drives have the hidden EFI partition containing the Clover EFI folders?
Frankly it has been so long since I used Clover that I can't be of much assistance.
Keep those backup drives, as the failure to boot is more likely due to a bad Clover EFI folder than a problem with any of the SSDs. When you resolve the boot problem those drives should still be useable.
Perhaps start fresh setting up a new Clover thumb drive to boot from. If I understand correctly you are attempting to install Mojave? If the drive you are trying to install to is not corrupted, installing Mojave will simply update the OS and not disturb any user data or apps.