I have three active Macs: an older MaPro tower (on Mojave) with 4 Internal HDDs; a Mac Mini M1 on Monterey 12.2; and a MacBool Pro M1 Pro also on Monterey 12.2. I am the sole operator and I must be able see, read and write to any connected machine

I have managed to achieve what I needed to do (via SUDO; followed by a total shut-down & restart of all three computers and the web Modem/Browser as well).

I can now access all files on each of the three computers and on the six connected HDDs and SSDs; from any one of the other computers.

I eventually figured out a way to be able to download and work on any image stored on any of the seven mounted SSDs and HDDs (in three networked Macs) in which the file is stored.

The solution involved invoking SUDO status on each computer in turn. 

I could then re-name to ensure that all machines and drives used identical Users and Accounts; and that the contents of all drives were “Shared”.

I can now see all seven drives listed under the  Network on any of my computers and, for convenience, make icons of those Drives visible on the Desktops of all computers.

I then disabled SUDO on each computer.

Now, a simple click on its icon displays the full contents of that Drive so any of my images can be opened, and edited, from any of the networked computers.

I have added this note in the hope that it may be useful to anyone else who wants to be able to connect to any of their files from a distant computer.

The files to which I need access are my multi-thousands of photographs and other personally saved files of various kinds including production output files from professional programs from Adobe and others.

(I am a professional photographer and the Creative Director for an advertising agency so these files are extremely important to me!)