There is nothing inherently wrong with your translation: TOU DIABOLOU is
genitive singular and could depend upon TOU PATROS as you have understood
it. In the context, however, it makes more sense to understand TOU DIABOLOU
as being in apposition to TOU PATROS, so that we understand: "You are (=
derive) from (your) father, the devil."
Personally, I would prefer to set off TOU DIABOLOU in comma in the Greek
text, but I suppose the editors preferred to leave the ambiguity of the
construction open.
Carl W. Conrad
Department of Classics, Washington University
One Brookings Drive, St. Louis, MO, USA 63130
(314) 935-4018
cwconrad@artsci.wustl.edu OR cwc@oui.com
WWW: http://www.artsci.wustl.edu/~cwconrad/