I've been pondering on an origination for Hesse-Engelburg, and have some ideas to run past people for suggestion.
I'm thinking perhaps it was once owned by one of the minor Hessian lines, but at some prior point that line rebelled against the Holy Roman Emperor, and the Blauerwolf family, then perhaps a Knight or at most a Baron, were granted recognition as Furst of the territory for their support in the fight to overcome the Hessian rebel.
It's a loose framework, and I may change it significantly, but some folks with a more detailed knowledge of earlier European history could perhaps suggest whether this is reasonable, and what time period might work for there to be such a conflict?
The Defenestrated Kolbold
47 minutes ago