Hey, what a good project to get stuck into .... but first you should determine which part(s) of each iMac are 'dead'. If you haven't already got one, buy yourself a multimeter for testing circuits and power supply. That last feature is certainly a "known issue" with the G5 iMacs so I'd start with those.
Second - if you can get at the hard drives and remove them, you can test them to an operating Mac with an adaptor (see att).
There are some good videos on YouTube about opening up an iMac - take a look at those. When you open up the iMac have your digital camera handy to photograph exactly where everything goes.
Good luck!