As I expect was meant to happen, I bribed my way in the locked front door only to get thrown out. Now it says to find a way to sneak back in, and leads me to the cellar doors in the rear. I am inside and with the help of a detect life spell and some very weak "hardly working at all even when standing still" invisibility potions, I make my way to the second floor and follow the quest arrow through the bedroom door. Strangely, its the arrow not the door symbol, but I follow it anyway.
I am in the bedroom and the arrow leads me out another door to a very tiny balcony. From there, all I have is the door symbol, that leads behind the house again to the cellar doors. When I went in through the cellar the quest stage - Search for a way to get in unnoticed - did not fill in as if it had been accomplished.
I'll go tackle one of the easier black stones for now and hope this will fall into place later, but if anyone has any advice it would be appreciated