SketchUp doesn't like using networked resources. The best I can think of is to set up your library, save it to cloud (or server) space and updated using a 3rd party app, run the same 3rd party app on the other machines pointing to the cloud (or server) space thus ensuring all libraries stay synchronised.

Ha i found myself the way. I followed your explanation until point 9. Then i opened the path, and copied into the new materials folder the .skm files, re launched Sketchup and it's done!