It is assumed most of the younger generation of continental royals attended. So Haakon, Mette-Marit and Martha-Louise from Norway, Victoria and Daniel from Sweden. Frederik and Mary from Denmark, Philippe and Mathilde from Belgium, Henri, Maria Theresa and i believe Stephanie from Luxembourg, Felipe and Letitia from Spain.
There were no reports over a British delegation. If so it would most likely have been the Wessex'. There also were plenty of German relatives but we have no idea who.