Download macOS Installer.dmg file
Download on the first machine.  
When complete, the Installer will auto-launch.  
Quit it.  


The Installer is in /Applications/ and has the name Install macOS Sierra. [BTW it's not a .dmg, but an .app file]

Copy it to a safe place; after install it will be auto-deleted from Applications.

The copy can then be used on any other machine. Drop into the Applications folder on that machine &amp; launch.