With that much data written to the hard drive, henceforth recovery drive, there is virtually zero chance of either of you recovering any missing files. You can buy
Stellar Phoenix for Mac and try recovering them. This is the best data recovery program for OS X I can think of. It is far more thorough than Data Rescue and Disk Warrior.
If you have a Windows computer then
Nucleus Kernel Mac is the best of all (it only runs in Windows and needs to be running Windows natively).
First off stop using those computers immediately every second they are turned on and booted off the recovery drive the odds of recovery get worse.
What you will need. The data recovery software, and a destination drive you can boot off of other than the recovery drive.
Boot off the destination. If necessary you will have to buy a new hard drive if you don't have any spares and install Mac OS X. It is advisable that this drive be larger than the recovery drive (if I recall correctly I think Stellar Phoenix requires this). The recovery process can result in duplication of files as folder structure is often lost or only partially intact on deleted files.
Once you are booted off the destination drive. You can use your recovery software to access the recovery drive. Then let it perform a formatted media/lost file recovery scan. This can take many hours possible a couple days if the hard drive is having problems. So disable sleep in the energy saver in the preference pane of System Preferences. It is OK to let the screen sleep just not the whole computer or hard drives.
When the scan is complete you will be shown all the files found this will be both currently available and deleted. The files you are looking for probably will not be in the folder it was originally stored in. Instead they will likely be spread out amongst many randomly generated folders. Of those you do find many will likely be corrupted or hold zero data. This could be because they were partially written over or fragmented. There is nothing you can do for them.
