The Luxembourg newspaper, Tageblatt, has nearly 240 photos of Archduke Christian and Archduchess Adelaide's wedding with nary a foreign royal in sight, apart from the Luxembourg Grand Ducal family, and Prince Philipp and Princess Isabelle of Liechtenstein. Prince Philipp is the elder brother of Prince Nikolaus who is married to Princess Margaretha of Luxembourg, younger sister of Archduchess Marie Astrid.
Nearly 1300 were inside the Cathedral for the ceremony, but there are mentions of European royals who are not first or second cousins of the groom. Could this be because Christoph is the second son (and third child), and the younger sons do not have as grand a wedding as the eldest son? Archduke Christoph's wedding took place in France in a basilica, not a tiny Roman Catholic church in Washington, D.C. Only a few hundred could squeeze into St. Mary's Church in Chinatown. The Basilica of St. Epvre can seat at least 1300 people.
The royal guests who did travel to Washington, D.C., included members of the groom's maternal and paternal cousins, as well as the Duchess of Croy and her son, Hereditary Prince Carl Philipp (Germany), the Duke and Duchess of Braganza (Portugal), the Prince and Princess of Löwenstein-Wertheim-Rosenberg (Germany) and Princess Marie Louise of Bulgaria and her husband (New Jersey).
The gala reception was held at the city hall in Nancy. Dinner and dancing! The Hereditary Grand Duchess of Luxembourg apparently did not want to draw attention to herself!
and more photos - on the Grand Ducal Court's official website: the official photographer, Jean-Claude Ernst, was also in Washington, D.C.