Attic/upper floor with internal rooms

Hello everyone,

with the renovation of my upper floor, the "ideal" course of the vapor barrier(s) is unfortunately not quite clear.

So far, the upper floor was separated. There was a heated living room and an unheated attic. The roofer who installed the new windows gave my wife the idea to leave half of the attic "open" (beams remain visible). The rafters in the "open area" will be doubled and the vapor barrier will be laid over the gable to the other side.

Problem:
In one part of the room, there are still the walls of the hallway and a bathroom. Image 2 shows the part of the roof that is actually supposed to be continued up to the gable as well. The boards are to be dismantled back to the wall and then built up to the roof after drywall construction.
Image 3 shows the attic part in the same direction, which is to remain. The right 4 fields are my problem, as underneath here are the hallway and the bathroom.
Image 5 shows the access to the fields and images 3 and 4 the corresponding exits from the attic.

Here the connection is not clear to me.

Is it necessary to install 2 chambers? That is, a "warm" and a "cold" attic area?
Do I save, with logical losses, only the part of the attic to the connection below and close the vapor barrier at the top and start again at the bottom?
How would you solve this?

P.S. Opening the bathroom ceiling is not an option, the bathroom was renovated 2 years ago (before our time) ;)
P.P.S I hope my problem is somewhat understandable...

Regards, Tobi