Following Olrich's bout of madness, the first thing Konrad did was to have Krann bring Adelar's Essence Concealing Ring to Yvonne.
The second one was to secure Nils and take all of Olrich's children into captivity. The reason was simple. Attempting to take all of the women away, one after the other, was a pipe dream. He could only rely on Yvonne to buy time while setting up a foolproof plan.
Of his nine children, there were two Olrich couldn't afford to lose:
Nils and Elmar.
If they died, it had to be by his hand. As for the five that now remained, while Konrad realized that their lives mattered not, he could use their deaths to showcase his seriousness.
Krann currently held them all and used Flesh Transformation to have three helpless eunuchs assume the shape of Nils, Elmar, and Holger. The real ones were pocketed. If need be, they would first kill the real princes to cover for the false ones.