Brother-Sister relationship
Did the thought cross anyone else's mind that maybe the uncle and mom had a weird relationship growing up? They seemed extremely close and almost intimate at times. They also both had to see shrinks at some point in their lives (I *think* the uncle said something about having had to see someone). No doubt, he was really the only "normal", grounded character in the movie and very likeable. However, with the way he reacted to Joshua at times and at the end when he really showed no odd reaction to Joshua's song...it made me wonder. Also, how he made some comment about sisters coming in handy (or something like that). So while Joshua originally wanted Lily out of the picture, maybe in time, he might develop an extremely close relationship with her. If this were to happen (say if there were a sequal), I could easily see Lily either becoming demented like he is or the total opposite -the one thing that keeps him grounded and acts as his moral compass.
I could be totally off in this thought because I, unfortunately, had several distractions going on during the movie, but just figured I'd throw it out there.