Idea for separating a floor in the house

Hello everyone,

I am looking for ideas for the following concern. I will be renovating a floor (130m2) in my grandparents' house.

Since we want to separate the floor, we are currently searching for ideas on how to do this best. The following points should be considered.
- the separation will be done in front of the hallway, as the staircase must of course remain accessible, since there is a 2nd floor
- it should be relatively opaque, but still allow light to pass through, as the only windows are in the staircase (one balcony door and 3 large windows).
- it should be lockable with a door

What would you recommend? The height is 2.60m, the width 2.35m.

Thanks in advance,

Best regards

First and third point are understandable. I do not understand point 2. Perhaps you have a drawing from the outside and the floor plan of the staircase? But if the third floor is being renovated, and the first and second remain with the grandparents, wouldn't it be possible to add your separate entrance on any other side?!
Regards, Yvonne