I have never seen any reliable information suggesting that the Claude killed by the Iroquois was the son of Claude and the brother of Pierre Marcoux, ancestor of virtually all Marcoux in North America. I have occasionally seen that idea mentioned on web sites but considered it unreliable. Until some good source turns up, I think its prudent to consider that idea hypothetical.
My own information on the unfortunate Claude Marcou and other Marcoux is at my web site www.eMarcoux.net and in the associated emarcouxnet database on WorldConnect (contains about 3500 Marcoux individuals).
I've taken the liberty of adding your line to this database. It was mostly all completely new information to me. If you wish to share any further information on this line, I'd love to hear from you.
Douglas J. Graham Rockville, MD (firstname.lastname@example.org)