I also bring stuff home from work, and I also work on other people's computer as well (and who knows what can be on them).
Look, its good you want to be virus free, but you have to realize that for a home environment (not a commercial environment) that using a good AV just for your PC's will do most of the leg work in finding and stopping viruses. Plus you have to "run" viruses in order for you to them catch them and infect other computers; which most AV will stop before it gets to that point.
If you feel uneasy with working on people's junk, then do a virus scan of their PC over the network or use a bootable virus scanner software on a usb stick. PC viruses are still mostly dependent on your action to spread.
WHS is mostly for backup and data storage, not running scripts, programs or other pieces of software. Putting AV on a WHS box for that application is like going around and wearing a glove and mask all the time because you are worried about catching the cold.