Just physically unplug the C SATA and D SATA from the machine. Then when you boot the live ISO there’s only one drive available and only one to install to. No potential to mess it up and no potential to place the boot loader on the wrong efi partition.
Edit: Once the drives are disconnected, it’s the normal install process. This is how I always install my multi-boot systems, it removes me from the equation for error (mostly).