To continue this mystery I add the following questions..
1. The Guards - Were they human? The daughters didn't like having the guards all the time and the guards were displeased when they were relieved from their duty. Maybe something happened?
2. The nightblood, the lamia, and the robots. These are all creatures from the shadowed man faction and are in Nek Castle. What connection is there? Perhaps this is why he Everling is trapping adventurers into his castle? They need more test subjects it seems. Maybe, just some of these Everlings are puppets inhabited by shadowed men?
3. One of the sisters had a pet bear. Shadowed men often inhabit bears. Thus the castle was ifniltrated.