Prince is not a title in France. Only members of former royal and imperial families have the rank of prince : Bourbon, Bonaparte, Orleans, (The same as in Britain).
The Head of the de Broglie family is duc de Broglie. He is "prince de Broglie" only par courtoisie in France. Which means he is not prince.
Beeing "prince du Saint Empire", he may call himself prince in Belgium, Germany, Austria, Hungary, Slovenia, Croatia and Italy, but not in France.
His wife is "princesse de Broglie" par courtoisie. No other Broglie is prince.
A "prince du Saint Empire" ranks under every duke in France.
(reference : Bottin Mondain 2005, p 1862)