On the ground floor, we would like to introduce a simpler plan with clear distinction between family and guest area/circulation, with minimal intervention.
We propose that the spiral staircase going to the guest attic on the 2nd floor starts from the ground floor, where the kitchen is. In this way, bedrooms above are not disturbed by guest circulation, while the new opening will bring more lights to the kitchen and the 2nd bedroom hallway (you can put glass wall on the 2nd floor hallway and create a skylight above this spiral stairs).
We expand the +20 cm floor up to the entrance area, forming a sense of 'foyer' in front of front door, so the living area is now larger and higher than the rest of the room. And then we remodel the stairs, so the shape now is a U shape, coming from the living room. The step is also reduced due to the raised floor from foyer to living.
We also put the powder room below the main linear staircase (the headroom is enough to accommodate +2.2m ceiling) , and enlarge the kitchen. The staircase functions as a light well-since there is a new window above, and we use white 3D wall matt 80 (ex. Atlas Concorde) as background wall at the staircase, continuing from ground floor to upper floor. We suggest to place dry garden (white pebble stones) and succulent plants below the staircase, as well as putting some indoor plants to bring the nature into the house.
For 2nd floor: We basically enlarge the master suite and master bath, as well as reducing the hallway. In the master bedroom, the corner where you have seating area (next to spiral stairs) can be converted into a small baby room (for your 1 year old kid), if necessary. (For now, we draw to have a larger master suite with corner seating). Since the shared/common bath is located quite far near kitchenette, we propose to that kids can use your bathroom too, especially at night. Therefore, for proximity usage, we propose to create a new double door to the bedroom hallway to secure the sleeping zone at night, while your kids can still access your room and bathroom. We think that being close to your young kids would be better. If later the kids are growing, you can demolish this double door. However, the new door is only for additional measure. Without a door, the kids are also welcome to hang out in the master suite, for sure!
The family room is an open space, functions as family seating, dining, and piano area. The home office is only a space with shelving partition/divider, we don't block it with walls in order to bring more lights and air ventilation to the adjacent rooms. We also add a glass door from the kitchen to the bbq terrace, just in case you need to serve the ingredients from there, without having to cross the home office/study /library zone.
Hope that our proposed design and plan will spark more ideas for you. If you would like to develop it further, we will be more than happy to hear your feedback. Thanks!