Both Lutz and Deid accidentaly insulted an archduke of Ehrenfest lol
Ferdinand knows nothing about Rozemyne having the remaining two thirds. I think his fey paper copy is meant to help the royals keep the country running a little bit longer until they get their own, plus it's a bargaining chip.
Though Rozemyne could probably absorb its knowledge with a quick copy/paste...
Eglantine and Anastasius implied that underage marriage would be possible with the Zent's explicit approval