No the King would be the Duke then his Eldest son would be the Crown Prince, But Given the MC achievement and his Marriage to Anna, the Highest Rank he could Possibly Attain here. would be either Marquess or Possibly Duke if they manage to Subdue(Conquer) more lands.
i hope she know War strategies. or she got a very clever Scheme where she can also Brainwash the Emperor of the Enemy kingdom and other Countries leader to Unite them Against the Ramslett. cause if not then what she do is Equate to her Kingdoms Suicide.
and the irony for this is he did it to protect her from her father and later he plan to save her from him and later apologies and maybe cut anything relationship with them doing so curtail the fathers ambition to used his Noble peerage of Duke. and now she's engage with the crown prince making...