Fun fact, the De Lannoys share their surname with the Delanos, as in Franklin Delano Roosevelt (although not the only presidents related to that family, and the original Delano is not related to the nobility)
Delannoy is a relatively common name from northern France, Lannoy is a commune, or more commonly a place (modern french l'aulnaie) planted with aulnes (Alders). Same meaning, different graphy, for Delaunay, as in Delaunay triangulation.
