I believe boredom and or the daredevil impulse people with chronic conditions often have as the reasons and it could have been both together!
But in reading this thread, it seems it was something that he did with a playmate more than once. in his diary , Alexis says they did it for "ages" .In the movie N&A, they make it seem it was out of the blue and a direct attempt to alter events...it's an interesting question...because so often events are made up of many things and in a combination that we , over 90 years later , might not be able to see.
As for who is who in the amazing photos Nemos posted in Posts: 461 on page 6
I would say left to right

Tatiana, Alexis, Nicholas, guard

Anastasia, Olga, Marie
and I believe a case can be made this was the same day of the roof photo,where they are sitting in a line, based on the clothing
(which seem a complete match) and just the fact that photos are being taken. I don't believe it was an every day event like before captivity .
These photos are so evocative...the crushing boredom is palpable