There’s a lot here but i need to point out the time difference. 100 years down below is 3000 years on the surface. So if they’ve been in the 6th layer for a day, it’s already been a month up above. If they’ve been for 2 weeks, it’s already been a year.
and that’s only layer 6. Layer 7 is probably exponentially more. I’m guessing at least 100 times faster than the surface.
I’m not sure how long this journey has actually been but I see an epilogue where they make it to the surface in time to see that their friends from the orphanage are all old men. Or one of them becomes a white whistle and comes down to meet them.