Quote -      Select the parent prop.  Click the + to save it as a prop to the library, but use the select subset button when prompted for a name, and tick all of the props you want.  A single prop file will be saved to the library, but it will consist of all of the chosen props, parented in the same hierarchy you had when you saved them.  And they will all still have their own material.

 

That I do know. See my example respond to Jaajger for a better explanation.