I'd take the hard drives out and then offer the laptops on Ebay for spares
Take a look - theres quite an active market there. Depending on the model you could get £50 or more for each. Once broken apart the plastics alone are worth that, and then theres value in the motherboard as a spare....
regarding the hard drives
use this program to nuke the data
Darik's Boot And Nuke | Hard Drive Disk Wipe and Data Clearing then either take them apart and scratch the platter
or you could just stick a drill through the middle in several places
FWIW most non-ferrous metal recyclers are geared up to shredding hard drives