331L: War Kids Seek Treasure

The book I am trying to identify was written over 60 years ago, and it features a group of children ages five or so through 14, or thereabouts.  They have been sent to the country because of the Second World War, and they become convinced there is lost treasure in the vicinity.  The only scene I remember takes place in church.  The younger kids are shocked and scandalized during the service as the collection basket enters their pew.  The eldest, instead of putting a coin in, pulls one out!  This is their first real clue.  The coin turns out to be a genuine gold doubloon.  The eldest boy may have been named Emil.  Do you know which book this is?

325P: Cereus Cactus Blooms During Anschluss

I’m looking for a middle school book, what would be YA these days, but they didn’t have YA in the 60’s, when I most likely read this book.  The protagonist is a girl, part of whose attention is focused on a night-blooming cereus cactus party that her family will hold on the night that the plant blooms.  Surrounding this domestic detail are the events leading up to the Anschluss and the threat that the Anschluss presents.

319A: Aeronautical Adventures

1930s or 1940s adventure books (of short stories) for boys featuring airplanes.  I remember a story that featured a crew of men attempting a record breaking non-stop (transcontinental? Transatlantic?) flight, in a 3 engine plane that could be refueled midair.  I remember a scene where one engine was shut down for in flight maintenance. 

One story featured two pilots flying an old biplane in a barnstorming content that was won because the co-pilot dumped itching powder down his partner's back.  Another featured WWII aircrew captured by Germans and they manage to escape and steal a German plane equipped with skis for the snow.  These books had belonged to my father, and were probably given to him by his uncle, who was a pilot.