This is the result of good parenting...
'Rents are doing something right with that girl.
When siblings must share a room but need some privacy too. That's a big room but it could scale down.
Yes, a fair amount of work but easier than splitting the room and another door.
The fourth corner of the bottom bed could have a post or ladder so the upper wouldn't have to be as structural.
Or just a post, or two posts, one on each open corner.
Pretty clever. I wonder if it's just an island,, not dividing the window.
There's only one open corner that matters, on the bottom, the top corner can be open as it's not holding anything up. I think it's an island.