I'm pretty sure it's
The numbers encode, somewhat amazingly,
and to combine two of them along the arrows, you just
which, by some bizarre cosmic coincidence, seems to produce another suitable member in the set quite often. Wow.
(The kids require attention, so I'll type in the rest of the details soon.)
EDIT: Here are the promised details (for some ...
One group contains...
And the other contains...
Explanation of each word:
And a quick mockup of how the image spatially relates to the puzzle, as suggested by the hints:
Here's your list with most initials and majors in place. I also added their ages and their personal best of tetris lines scored in a single game. (I think those were some of your interview questions.)
You seem to have interviewed both John and Frederick twice, and I think Gabriel's initial should actually be G. I couldn't figure out your mom's initial, nor ...
@athin has found the mathematical pattern in the sequence and created a useful general way to display it pictorially (go see their post and upvote). However, a slightly more accurate diagrammatic rendering would be as follows:
This is because the sequence reflects:
The significance of 23 March in the hints is that:
The pattern emerges as:
Why does the ...
You can build a structure something along the lines of a da Vinci bridge, where the weight of the structure itself keeps it from falling apart:
It's easiest to build on the tabletop; you can then pick it up by the bottom nail, watch how gravity locks the structure into place, and then balance the whole on the vertical nail.
These clues all point towards:
In case you're interested, the breakthrough for me finally came with Clue 12, coupled with your throwaway comment to @Sid saying that your younger sister solved it pretty quickly!
The first thing to notice here is that:
How does this produce the locations turned up by your 'hacked' Google Maps?
So, how about that trip to POLAND? Well, consider that:
One final diagram showing the entire solution:
Did she accidentally leave
for her flat?
Or did someone maybe
Either reason would account for
(Probably not the correct answer, since neither reason quite explains the two extra notes in the music, nor why the first and second lines have been swapped. But with the chance to put all those music puns into an answer, it's not like that's going to stop me ...
How about this arrangement:
If all of these categories are correct, then the municipality which would satisfy all 7 categories is:
PS It's also worth noting from the comments that there are a few alternative linguistic categories that would also work to produce the same final connecting municipality...
You are going to:
And the Safe combo is:
I had no idea where to start with this, so did some cryptanalysis. The Index of Coincidence was $0.04082$ suggesting a polyalphabetic cipher (therefore likely vigenere), and running probable key lengths suggested that the most likely key length would be 8. Now things started to fall into place!
The first important ...