@Kier
I just found a mistake on my reread of P4V1.
During the "The Better Grade Committee" chapter, Hartmut introduces himself as the second son of Ottilie, when he was earlier introduced as the youngest son of Ottilie by Rihyarda. This is confirmed in P5V2 when Leberecht, Ottilie's husband, says that Hartmut is his youngest son. And the Fanbook 2 family tree show that Ottilie and Leberecht have 3 sons, not 2 (including Hartmut).
The passage in the "The Better Grade Committee" chapter is as follow:
Hartmut stepped forward after Traugott. “I have been awaiting your return ever since you first instructed us to gather information in the Royal Academy, Lady Rozemyne. I am overjoyed to serve you,” he said, his amber eyes crinkled in a bright, peaceful smile. His way of speaking made him sound exactly like Justus, though his noticeably red hair meant he probably wasn’t as suited to stealthy reconnaissance. He was Ottilie’s second son, a fourteen-year-old apprentice archscholar in his fifth year.
It should be either Ottilie’s third son, or Ottilie’s youngest son.
The japanese version I was linked to appears to be:
まるでユストクスのようなことを言った。だが、ユストクスと違って特徴的な朱色の髪が諜報活動には向かない。にこにことした穏やかな雰囲気の中に、茶目っ気を感じる橙だいだい のような明るい瞳がある。上級貴族の文官見習いで十四歳の五年生、オティーリエの末息子だそうだ。