While siblings vs. cousins may not be the same thing, is the distinction relevant? I am not aware of siblings marrying each other as a relatively recent common practice in Japan, but I have never thought of looking it up before. Is there someone who knows by chance? lol
Also, I stumbled through thepress release, and I think it says they are blood related. So that shoots down the step-sibling possibility (Does anyone remember the movie Clueless? lol).