Calibre from 2 different Macs, same Library

Hi,

I want to share my Calibre library with my son.
My iMac and my son's Macbook are connected, and I have shared Calibre Library, that I can see in the Finder.

Unfortunately I am not able to open the library with my son's Calibre.
First I have given write access (-> first bug solved), but even now Calibre is requesting to repair / update the database, with a blue status bar ongoing but not increasing.

I tried also to quit my own Calibre, to restore database, maintenance, with no benefit either

Thanks for your help