Have there been any other primary or secondary schools which have enrolled (future) monarchs from two separate countries within a single generation? It seems like quite the distinction for the school.
Future Monarchs from the same generation? Probably Eton and Harrow, internationally maybe Le Rosey. I think Knig Hussein of Jordan and Feisal of Iraq were at Harrow at the same time. And the Emir of Qatar was there was well.
Plenty of schools have had various royals from different countries attend at one time or another, but this one is certainly going to be looked at very closely now.