That is a good question indeed, it may be that they had lodgings there as many aristocratic families did.
As for Oliver actually being a Russell, it is documented somewhere on Google. Run a search on Oliver or The Dark Lanthorn. It is listed on his college's web site.
Have you visited Jim Churchyard's website? Google that as well. He hired an English administrator to peruse all of the documents and his reports I believe will add to the Elizabeth/Nicholas equation.
As for the DNA research, there is another Project, The St. John Family, which I too am a participant of, they have an English St. John who matches descendants ofThomas St. John who arrived in the Virginia Colonies and as far as we know are not kinsmen to Matthias. I too had thought that Richard, and not Oliver, was our best shot.
I also wanted to treat the Huguenot theory. Being that Sension sounds like a phonetic spelling of the french, "Saint-Jean" or other variant spellings, it made a good case. But if Matthias first language was indeed french, how did he wind up wedding a lass from Berkshire named Mary Tinker? Matthias is not mentioned on any ship rolls either, which complicates things further.