iMac wiped clean, no install disc
Unless your MacBook Pro lacks a FireWire port, you can use Target Disk Mode to have the iMac reboot and act as a FireWire drive.

From there, you could use Disk Utility (or Carbon Copy Cloner or SuperDuper or other tools) to make a bootable copy of the MBP's OS onto the iMac's drive.

Alternatively, you might buy Mountain Lion or use a past Lion purchase from the app store to download an installer and run it from the MBP. You could choose to install the OS onto the "external drive" that is the iMac. Then you could chain the second iMac (or repeat this activity).

It really depends what OS you want and can run on the iMacs.

Your first step is to run the serial number of the iMacs to this page and see what Apple's service name for each Mac. From there, you will know what OS shipped and if the Mac can run Lion or Mountain Lion.


http://support.apple.com/manuals/#


Just enter the serial number in the address bar past the # or enter it into the form on the web page. You can always order replacement media from Apple, but there will be a charge for that. The other suggestions to buy a retail packaging DVD to install will likely be an inexpensive way to acquire an install OS once you have determined what OS can run and which OS you want to run.