He's a fool, but he's a fool with power. His blood ties him to the castle and the seal, which allowed him to loosen its hold on the Vernacht. The castle is sentient after a fashion, and will report to him what it sees. His servants can sense magic and heal in a fashion similar to what you said you saw the Vernacht do. And when those who die here will simply revive after a time...

[Sync shrugs. They need to get rid of the Lord, but it's not as easy as one would think]