They should've used the escape scroll the moment he realized who she was. I thought it was a Chekhov's gun that would be used at a time like this, but I guess it was just a useless detail to be conveniently forgotten, because bad writing.
So the writing had him sell his soul to let them escape a predicament they could have escaped at the right time or even avoided? Forced drama it is. I am left with the feeling that whatever moral his uncle/stepdad's story was supposed to have, he has horribly misinterpreted. It feels like he did exactly the opposite of what the story was supposed to teach him.
The manga states near the end of the previous volume how the true horror begins in the second floor of this dungeon, well, I guess for me this arc is also where the story truly nosedives, not that it wasn't already going bad before.