Provided the old computers turn on, power the comptuer(s) up and plug in a usb hard drive or flash drive. Then select and drag, or copy and paste the files to the drive. Then plug into the other computer and repeat the process.
For data destruction there are free software programs you can run to wipe the data out, but the best way and less technical way would be to remove the hard drive and smash it with a chisel, hammer or use a drive to put holes in it.
Also you can't throw electronics away, you will need to recycle them. Do a web search for your area. Also some places can either wipe the data for you or destroy the disk for a small fee.