Batch Import tool in the Material Organizer drop-down helps import materials from a family file to some others in batch.
After the ribbon button is clicked, it pops up a dialog for file picking.
Then the following dialog will appear to ask for which family to import materials from.
If the OK button is clicked, materials in the family file will be imported accordingly into other files one by one. A progress bar will show how many files in total, which file is currently being processed, and what remaining time may be. An information box will finally show what have happened.