Erase RAID-1

I have never used software RAIDs, but I think something started wrong here, but realize that I don't fully understand what you did or why.

But, just stretching for an idea, I think that you should have first split the RAID by removing one of the drives from that RAID set first, so that both drives appear individually in the Finder again outside of any RAID, then performed an erase of each drive individually, if that was your intention.

"5.    Tried to ERASE the first RAID-A.

6.    Now, RAID-A is not viewable in FINDER or DISK UTILITY."

What drives show up in /Volumes now?

from Finder, Go, Go to Folder... cmd-shift-G

Sounds like you have all the data in another safe place, not on any of those four drives. And you just want to rebuild the new drives into a new RAID-1...

8.  Moved all data from all four drives

...

I would like to ERASE all four drives and make the two new ones into a RAID-1.

shut down the computer, disconnect all the drives. Reboot, then connect only one drive at a time. Try to reformat with Disk Utility one drive at a time. If you can see one drive individually, and then the other drive individually, then try both at the same time and try to make the new RAID-1 set again.

If these external drives are four individual separate drives, then that is not good for any type of RAID as they are more likely to drop one of the drives from the array. If you have a single enclosure supporting two drives which are being made into a RAID, then that is much better, however, even this setup can still have a drive drop from the array if it doesn't respond in a certain amount of time determined by the RAID controller (in this case the software RAID managing the drives).

Plus you never mentioned the exact model Mac, or macOS, plus no mention of the RAID enclosure or drives and their hardware configurations. All of this is extremely important and one reason why @rkaufmann87 provided the link about writing a good question. Apple Silicon Macs are not compatible with all external devices (especially some older ones), plus even macOS can play a role here.

Disconnect all other external devices in case one of them is causing a problem.

Within Disk Utility make sure the physical drives are shown on the left pane of Disk Utility. Within Disk Utility you may need to click "View" and select "Show All Devices" before the physical drives appear on the left pane of Disk Utility. If a drive does not appear here, then it sounds like it at the very least dropped from the bus for whatever reason. I've seen a lot of forum posts on here where people have had their external drives drop unexpectedly (most times resolved by unchecking the macOS setting "Put drive to sleep when possible"...used to be available under the Battery or Energy Saver System Preferences).

As for erasing a drive which has been part of a RAID, you either need to use the RAID software to remove that physical drive from the array, or you need to zero out the beginning of the drive where the RAID information is stored on the drive. By writing zeroes to the beginning of the physical drive the partition table is destroyed along with an area where some other items like RAID information is also stored. After doing this, the drive will appear "blank" and unused like from the factory when purchasing a bare drive. Disk Utility can then be used to Erase the drive as you wish. I don't have time right now to give instructions on how to write zeroes to the beginning of the drive as it involves using the command line...writing instructions for someone unfamiliar with the command line is time consuming as extreme care must be taken (writing the instructions and following the instructions, or the wrong drive & data may be destroyed). Connecting the drive to a Windows system may be able to get rid of this information when Windows partitions & formats the drive (not sure if the RAID information will be removed as I never tried it, but there is a chance it will).

Writing an effective Apple Support Communities Question