Problems with my MBP

Those are just virtual volumes for the macOS installer, just ignore them they are not a problem.

If you want to perform a clean install by erasing the whole drive, then I would highly recommend creating a bootable macOS 10.13 High Sierra USB installer now while you still can by using the instructions in the following Apple article:

Create a bootable installer for macOS - Apple Support

You should also be able to use Internet Recovery Mode (Command + Option + R) to access the online macOS installer as well, but some people have local network issues which can prevent this option from working which is why I recommend having the USB installer handy (plus it should be faster & more reliable than Internet Recovery).

It is best to erase the whole physical drive as GUID partition and MacOS Extended (Journaled).

How to reinstall macOS - Apple Support

Of course you should make sure to have a good backup of any important data before erasing the drive.

DanWan wrote:

1° While in my new Macs my Apple ID works fine in this machine the Mail software tells me the passweord is wrong.

Can it be hiding in one of those various invisible partition as such:

I don't understand exactly what you are asking here.

I don't know anything about Mail and how it may or may not work on such an old OS. The Internet & online services change over time while macOS 10.13 High Sierra has been stagnant for many years now so it is not surprising that access to some online services may no longer work.