Howdy, sure seems this should be simpler... Take each laptops requirement of voltage & current: most modern ones are 18-20+V @ 1.5-3A. Think diode drops as "spacers" 1N5400s are ~ .8V @ 3A, 1N5420s are ~ .2V @ 3A (schottky).
I'd start with a couple more 5400s (And one set of 4X5420s) than it should run on... the lowest reliable voltage / current yields lowest power (duh). Hook it up to one of laptops, then behave as a ladder: step up each 5820, then after 4 5820s, jump a 5400.
Try to boot the system on each voltage point, but do yourself a favor and hold F8(?) to keep it from trying to run Windows :: marginal voltage may (WILL) corrupt the hard drive.
Once reliable boot to menu occurs, let it go to Windows. Do this for each system....
It's just an idea, doesn't mean it's good G.H <<<)))