It sounds like the USB drive doesn't have the drivers to boot the other macs. :-(

The fastest path forward is to simply erase install a basic Snow Leopard OS onto the failed macs.

Don't bother with updates unless the installer forces you to get to a higher version than your 10.6 installer level.

Once you boot into OS X - you can still mount the USB and try clicking the package to execute the Lion upgrade program. I don't know if it runs mounted or needs to be copied to the internal boot drive.

There's a little uncertainty in my brain - so I don't want to write too much without making sure this makes sense to you.