Download OS update only once for all home computers
To quote Bryan Luby from "Re-use Mavericks install file"


  Download the update from the App Store. Once the file has finished downloading, check your Applications folder for the "Install OS X Mavericks" icon. Copy this installer to your other computers before going through the install process. The installer will delete itself after the install is finished.


I recommend distributing the file between computers via AirDrop (if all your computers support it) or via File Sharing (from the Sharing pane of System Preferences).

Note: Running the update from /Applications/Install OS X Mavericks.app will DELETE the installer upon completion! Be sure to distribute the file to all your machines before installing it.