Update...after all these months and much wrangling with the tangles.
His office now has only 2 users & the 'server' on the LAN anymore and in case it wasn't clear in either of my prior entries here:
Permissions help EXACTLY nothing in using local-only file shares for documents.
Until today Samba was in use and it can be stated as factual (IMO) that Libreoffice cannot correctly handle files shared via Samba.
Collabora Office is better by a goodly margin, but still trips over the strange permission problems - though it does so less than its ancestor, L.O.
NFS was never attempted after the hour or 2 that I wasted in trying to test it out brought me zero good results - all I got out of that attempt was a headache.
BUT:
I since got a suggestion to use SSHFS for file sharing over the LAN and did my usual sorts of widespread checking into it so as to compile the most consistent & pertinent info I could find before trying to impliment it.
So now I'm back again after spending almost my entire weekend doing computer fix-it stuff...including the part of that time used in setting up SSHFS as suggested.
It -IS- way better than Samba - but can also be much worse & I'll try to 'splain a little.
Getting it up & ready on the LAN's 'server' was indeed quite trivial.
Getting connected to it manually & testing it for ease of use at the 2 'client' ends also went very smoothly & was quite impressive, BUT:
There is the same lack of succinct & complete info (as Samba...) when it comes to automating it to reconnect at boot time, and I learned the hard way that this can result in the dreaded & inescapable emergency mode.
How did I get so lost ??
Out of the ~2 dozen sites I compiled connection info from - not even ONE mentioned that to add the mount points into fstab - you must FIRST have set up the proper key pairs so that it can authenticate - OR ELSE !!!!
Thank goodness for the Ventoy made USB tools stick that I have with Parted Magic which allowed me to comment out the offending lines & remove the dirty bit markings & then to have GParted make sure the partitions were indeed error free.
Then silly old me tried making a bash script to do the mounting...nope, that didn't work either, but at least it also didn't harm anything.
So - for the moment the needed connections are right, tight & do indeed function just like local file sharing & will just require manual reconnections after each reboot.
In the meantime I will try to work out the EXACT & needed details for correctly installing the key pairs - whilst I still really wish there was some other even simpler way to make it work...
Like maybe just from a single script with desktop icon to make it remount after a restart.
Thanks Again for any Helpful replies here !!