First thing:
RAID is not backup! RAID provides redundancy meaning if a drive fails things keep working. RAID doesn't protect from a controller failure, software problems, or if someone deletes the files.
What I've seen work to good effect is using USB drives, and just periodically copying over everything. You can rotate drives for better security
Now then, from the description of your situtation it looks like a NAS is ideal. You could make one yourself or buy a box like this:
http://www.newegg.com/Product/Produc...82E16822106001
Administration is through a web browser, it'll share files to all your computers, and it has built in raid support. Then all you have to do is regularly back up the NAS to a USB drive that you can put in a secure place.