From my own experience in doing two sword practice, I can't say there are many instances (just a few) wherein both swords are attacking simultaneously. I would think that doing so would diminish the applicability of using two swords wherein one can have both offensive and defensive movements at the same time by using the two swords in an appropriate manner. This is all just conjecture based on informal experience with doing two sword practice.
A person whom you might be able to contact is Kim Taylor
up at the University of Guelph in Canada who has studied Hyoho Niten Ichi Ryu kenjutsu (and also a very nice guy).
Perhaps Brian might be able to chime in according to what he's learned from Obata sensei? (I've had the pleasure of attending one of Obata sensei's shinkendo and aikido seminars and had a good time.)