Paul, have you seen this or do you know of this researcher? http://www.goodreads.com/story/show/22470-two-articles-on-the-old-n...
Also, are you new to Geni, or do you have an established tree? If you are new, then the best way to proceed would be to work with one of us who is a curator to find the existing profiles of those ancestors and add yourself to them and help to develop and solidify that lineage. Then simultaneously you can be building up your tree from yourself, and you can connect to that historical tree.
The way the curator system on Geni works is that there are public profiles (which generally form the historical tree) and then there are private profiles which consist of the closer generations to yourself. We curators work with users like yourself to develop the public, historical profiles, and we try to create one Master Profile (MP) for each historical figure and merge all the duplicates into that one. We encourage people to build up the information and data on the MPs to create a really solid genealogical database which is also encyclopedia-like in terms of biographical profiles.
One way to get started would be to start a Geni Project on the de Gernon surname. That would fit nicely under the Anglo Norman umbrella project that I oversee--would you like for me to do that and to add you as Project Collaborator, which would allow you extra editing and merging privileges on these profiles?