Regarding the girls below -
I want to hear from an audiologist with geology in his/her background before I settle my opinion and theory. But, for some reason it's ingrained in my brain (something learned early in life, I guess), there's a reason why choral singing sounds so wonderfully beautiful inside of an OLD church -most often Catholic- and it's because of the type of stone, shape of stones, and most specifically the positioning of the stone; aimed a tad upward, but ever so slightly - barely noticeable. Think Kate and Willz wedding, maybe, but I forget what their religion is technically called, or any Catholic Mass one can pull up on YT. Yeah, there are mics visible...but, that's for the tech used to record. Sitting in the presence of the choir wouldn't require a mic, imo.
Next to bring up would be the Acropolis Amphitheater and Red Rocks Amphitheater. The sounds from the stages are literally fed into the ears of audiences simply based from the earth's natural construction and location of audience - upwards and outwards. The sound is amplified because of that and is related to where we get the terms amplified and amphitheater. (Apologies as I've spent years listening to avid readers, one of which loves etymology).
Then, in the case of 1122, the house had the back built on later, as far as I know. I'm more inclined to help another find the price or location of those building materials than I am to say how to construct them. So, with my limited construction knowledge I do know a builder will have to add more weight-bearing capabilites to add a third story onto a two-story. While the house might be setup in a two-story plus two-story, just attached, kind-of-way...it's gonna require a mess ton of material for the first story to somehow bear the weight of the third, even if it's only by transference. More material to muffle a sound, including insulation designed for cold environments.
Having said all that, with that hill in the back I kinda view the setup of the house as a mini-proscenium, mini-theatre, or mini-amphitheatre with the sounds from floor two and floor three aimed at the back hill bouncing off that then being amplifed to everywhere else upwards and outwards, while the surviving girls were below where an orchestra pit would be in a live-theatre. Not in the orchestra pit, if you will, but below it/basement. That's typically where stuff for others shows will be and you can't hear anywhere near as much or as well as the audience who are upwards and outwards of the sounds.
Then add in, I'm under the impression the surviving girls may have travelled and returned from trips outside of Moscow? I might be wrong on that? But if I'm getting back from a road trip and smoke or drink upon my return/being twenty-something...yep, I'd fall asleep completely undisturbed by anything and everything muffled from above.
That's my theory thus far until I hear from an audiologist with geology in background give some views. I'd be all ears for that interview (har har har).