Yes, you can save from a mac laptop. I don't know about using the drive as a back up for both laptops. I don't use Time Machine, but I was curious.
You need the MacBook and the Mac Pro to be on a network. On the MacBook locate the Mac Pro as a shared device on the sidebar. Click on it, log in as the user (of the Mac Pro) and click on the target drive. Launch Time Machine. Select Set Up Time Machine, then click Select Backup disk. The drive from the Mac Pro that you mounted earlier should show up as an option.