Yep! Well, as canon as possible as in one can rarely be found without the other, and they have little interest in others, especially those who can't tell them apart, etc etc.
I don't know about the manga, but the fact that they shared a room and a bed in the anime kind of had me thinking that their whole twincest act wasn't really much of an act, besides the fact that they were playing it up for the crowds. Which I'm all for, frankly.
Anyway! If you're down for more plotting / chatting about it we could continue it here, or I could make a custom, or I'm available on AIM: scornfullysnape. :D
ediiiitt: I totally wrote all this out then you posted again. YAY! Hikaru! Boo! Phone deletes! I guess my previous message still stands though, with plotting, etc.