I pm'ed you Genie.
Now: quand elle venait se saoûler l' dedans de pathétique =lit. when she would come to get her "inside/within/inner self/soul" drunk with pathos/deep sadness/despair...
An argentier is a guy who deals with money -could be a treasury ministre/secretary but also a money seller or the like
un demi is a half pint of beer then un demi d'oubli is a half pint of beer meant to bring her forgetfulness
un accord here is a chord (both times)
the ghosts converse as friends about the bistrot and the piano
l'histoire enfermée dans le piano means the story shut/locked up within the piano