A corridor-access 100T% double-sided apartment is a contradiction and the problem is what to do withy the building volume either side of the corridor. it can be either made into single-sided apartments, incorporated into vertically adjacent apartments, or it have have one side as the lowest level of one apartment and the other side as the uppermost level of the other.
Solving the problem with horizontal asymmetry around the corridor invariably requires a second shaft. Here, the space between the upper kitchen cupboards and the ceiling is used to cross the corridor, avoiding a false ceiling in the lower kitchen.
Off the corridor are a studio, stairs down to a 2-bedroom apartment and stairs up to a 1-bedroom apartment. Alternatively, the 1-bed apartment can be downstairs and the 2-bed upstairs. Everything outside the dashed frame is arbitrary, as well as some things within it. The determining dimension is the total length of the stair plus the entrances at corridor level.
Remaining living areas can be reconfigured as studio apartments or combined with the volume of the studio to configure a single -sided maisonette. All or part of the volume of the existing studio apartment could be used to create a double-height living area for the apartment below.