Niel's instructions don't cover you 100%. You want to keep things on a different drive and there won't be a "shared" folder there. That's only on your main drive. You also have to migrate media and/or your library to a different drive using a special process or you will end up breaking all your music links.
You need to clearly state what you want to share. You can share just media or you can share your whole library structure. Sharing only media is safest but if you share a common media pool you will all have to keep each other appraised of additions (and deletions, because those too will affect everybody) from the pool. You have to be pretty trusting and coordinated on this. Alternatively you can make it so others can copy your media but you will each have your own copy of the file so if somebody else wants to change the name on a track it doesn't do it to the copy you use too. Of course this takes up the most space but is the safest. Which migration procedure to do will depend upon your answers to this section.
Finally, I hope you have a backup plan implemented on this. Nobody will be happy when that external drive fails and it all disappears.