Disposing of Multiple Macs/Keep Data

Hello, I was given about 8 old macbooks to dispose of at work. My boss gave me clear instructions to retain the data from each laptop and then wipe them/properly dispose of them. I know there are many ways to tackle this but what is the more convenient process. Is it possible to download the content of multiple macs on a large hard drive or would I have to buy one for each?

Also are there business out there that can help you do this? Is there a service available? Thank you!