As curious as it sounds, you should say Le Fanu the same way, for example, as
La Fontaine and le duc de
La Rochefoucauld because they are part and in front of family's name.
If there is a rationale behind the rule above
, I would bet for: Duroy
or Du Roy because Du now is in front and part of the name. (In the version mentioned below, Duroy is used).
Alex you can go here: (
http://www.ebooksgratuits.com/ebooks.php) and download this
http://www.ebooksgratuits.com/newsen...1289&format=so The source doc for "Bel-Ami Édition illustrée" so you can do a search for problematic names. BTW this a nice édition.
PS IMO (and you know that of course!), one good rule is to have the same names systematically across the novel.