You need a bootable disc, and your friend's MacBook install disks will not work for your MBP's.
Try google, there may be a way to create a bootable disk with your current disk. Also if you use carbon copy cloner and clone your hard drive to an external drive. That will be bootable and thus you'll be able to wipe the internal disk. Since you don't have the install disks, that may be an issue in selling, i.e., a new formatted hard drive w/o an OS on it.