Isis tells the truth. There is no way in hell that someone will copy something off the internet. Whenever I see a copyright symbol on art or something, I tend to think that person is paranoid. No one will be that desperate to steal, and even then, I would be more than honored if someone stole my work and published it--makes me have some credentials to fall upon, but even I wouldn't know of its existence.
However, if you intend for your story to be published, you'd better not post it on the internet, and if you do, delete all evidence of its existence. This one smart kid, before leaving this website indefinitely, eliminated every work of literature he posted. Seeing those empty topics does give me a void in my heart, but, now he won't be pestered if he wishes to get his work published.
You can't sue, but you can learn so much more about yourself through a critique. I say your brother goes for it.