Im assuiming your at the part where you play murder mystery. In that case, you have to be in Morgana's demense and talk to everyone there. Should be one person in every room besides the Main room. You do need Morgana's permission to explore her house but if you have talked to Dhena, then i think you have it.
You also have to confront them in a certain way. You have to find something that would incriminate them. I usually start with the cat lady and the gardner bull(his name starts with an E i think). Each person has a different story that contradicts someone else's story, meaning you can then take that evidence to them and see what they have to say. If you have done the questioning right you should end the investigation with Ard and Hana. Without spoiling more than I have that is essentially what you have to do to solve the case with Morgana. That is, in a perfect world at least. Any other issue you have with the quest is unfamiliar to me.