What the others have said.
I would attack it like this:
Go to the manufacturers website and check if Win 7 drivers are available for this model. If so grab them ALL and put them on a USB key.
When you get the laptops and other stuff make sure it's all there, keys, valid install media etc.
If all is good then I would either back up one of the laptops drives or swap out the drive with another spare one to use as a test mule.
Setup Windows 7, get all the drivers setup, make sure all the device in device manager are good without any problems. Do all the MS updates, install all the apps you want like Java / Flash etc. See my note below about MS Office.
Are they ALL the same model? If so you are in luck. You can use the first as a base for an image. You can run sysprep, specify the Out-of-box experience (OOBE). Shut it don and then get a backup utility to back the HDD image up to. Aomei Backupper is a free one, there are others that have a fairly low cost too. Back the image up to a USB drive, then using the backup utilities rescue media restore the image to the HDD, the original one if you swapped it out.
Boot the new image on the laptop, go through the mini-setup and check that all is OK. You will need to change the Windows key on each one, RIGHT click the Computer icon or go SYSTEM in control panel. Click on CHANGE PRODUCT KEY and enter a new key. You can make the MS Office part of the image or install it on each one. MS Office is a bit harder to enter a new key for so you may want to install each on separately. If you do each one separately then you will have to update them all too. I would update ONE and record what Office updates MS Updates wants to install and then look each patch up and download them from MS directly, save them to the USB drive and use them to update all the other Office installations, you will save a ton of download time that way.
If all goes to hell then you can always just plug the original HDD back in - which is why it's best to use a spare HDD. Or restore the laptop with the backup you made of the original. Contact the owner and back out of the deal.
I have to ask. WHY are they wanting to go back to Win 7? Is it the need for Win 7 Ultimate itself? Perhaps it's the lack of a Start Menu? If it's this then have them consider using a Start Menu replacement like Start8. It's what I use to make Win 8.1 palatable.