I think you are giving this too much depth. I regarded it as a mere but pleasant detail that adds to the character of Ketheric Thorm, showing that the whole family had deep flaws resulting in them being so corruptible. I also think that only the innkeep was his son, and I think it was outside marriage, as someone else pointed out. It is also a nice showcase of fight mechanics, as all of these encounters are unique in how you can resolve them and how the fights play out. I would have appreciated some kind of dialogue of Ketheric regarding them, just to explain his relationship. Like him explaining why their corruption is different/misguided/inferior to his and justifying his deeds, as an example.
No, considering how important family in the story of act 2 is this had too little depth.
