Is there any way to advance the quest using console commands so I can talk to the king? My last save is a while back and I really don't want to do it all over.
OK, this was probably my fault. While I was sneaking to the top floor, I destroyed one of the constructs on the exterior of the mansion. Maybe that turned everything inside permanently hostile. Reloaded an earlier save and used the rope bridge to get to the top floor instead. Now the disguise works.
Please disregard previous posts
I'm running a fully patched version of the game and the Arkemyr's Old Robes does not work for me either. Every imp and construct in the mansion is hostile, regardless of whether my MC is wearing the Robes. I snuck in through the bathhouse basement, FWIW.