You would have to report to Mardaneus to solve George's murder, but without specifically asking the vampire about him I don't think you will get that option. Even asking the vampire about George, though, some people have had problems reporting to Mardaneus about this if he had already moved to the council hall.
You can only explore the treasure room area once. Other than the strangely small amount of stuff to loot for a treasure room, the main point of the area is plot development (ie you learn that Janus found the Sword of Lies while playing, and became possessed).
You only get one invitation from Ralph, even though he says he will give you one for solving both of the quests he is involved in which can get you into the castle (plague and duke's murder). Also, after you have been to the castle you can not get invited back.
