Question about copyright

[saeto15.livejournal.com]

I recently started drawing characters and aliens from the book series "Animorphs", and the art was pretty well-received. So I was thinking about making some keychains and pins for an upcoming con, but I'm not sure about the copyright issue there.

The alien species are recognizable if you'd ever read the series (mostly the hork-bajir and andalites, as most of the rest were never illustrated), but the human characters are generic enough that you wouldn't really know who they are unless you had read the books. Only my art would be used on the keychains/pins, and I wouldn't be using the "Animorphs" logo or anything. I toyed with the idea of having short quotes on the back of the keychains for each character as well, but for right now what I'd be going with is a two-sided keychain for the kids with a morph on one side and a portrait on the other.

So, what do you guys think? Innocent enough that nobody would really care, or should I go with a different idea? Scholastic isn't even publishing the series anymore, much less making merchandise for it (the recent reprint was cancelled for apparent lack of interest) but they do still hold the copyright.