If I have grasped the situation objectively - financially, as I said, I am out of the picture - the apartment being discussed for sale is a "third" property in this game, so not identical with the one occupied until the move. I estimate the market for selling the inherited apartment in Berlin in such a way that an unfinished clearing out only significantly hinders the homestaging, but not the actual sale - at least if it doesn't have any major flaws.
Compared to competitors for the plot - but if I understood correctly, you are, in a broader sense, neighbors of the seller, this barnyard scent sympathy bonus is no joke - you have the strategic advantage of knowing (and he in turn knows how to handle the club of the de-designation procedure before the demolition of the hopefully too small living space). Overall, I see no reason for lethargy here, but also not for hysteria (and of course I am happy to accompany further planning). knows the way to me, to windows and to a self-organized heating engineer, and he is also a "fellow sufferer" regarding the marketing of a (although still self-used until the move) condominium. So you already have the necessary (as the hero of stones so nicely says) "nice people around you" ;-)