Floor plan optimization single-family house 2 full floors approx. 180 sqm

I would reconsider the kitchen layout, on the island you have no space to work. Possibly move the sink or stove to the other countertop. If this were my kitchen, I would make a tall cabinet wall (possibly with a storage niche) with a peninsula. But then you would have to see how big the island could be and whether the space is sufficient.

EG
I find the cloakroom area for 4 people too small.
I would remove the pantry.

Be sure to mark the furniture to scale at least once. The living area seems too small.

OG
The play corridor is used for everything but not for playing.
I like the suggestion to remove the small corridor.
If the traffic routes are bigger than the children's rooms, something is wrong.
Try to access the parents' area through the dressing room.

Have you tried a different staircase? Large corridor on the ground floor and upper floor. On the ground floor, a narrow corridor forms along the staircase. Does not feel spacious from the entrance.

To what extent a seating window would replace a bar counter, I do not follow - in my perception, these are not alternatives for the same purpose.

Are 51 cm depth enough for a wardrobe?

Why exactly fifty-one? - and no, the wardrobe is not too small in depth alone.
What do the 39 cm exterior wall thickness mean, what wall construction is intended there?

The large hallway upstairs is intended, among other things, to serve as a play area for the children.

There will only be an armchair in the hallway upstairs

The children push the armchair down the stairs, and the parents step on building blocks every evening? That is unrealistic. See

To what extent a seating window would replace a bar counter, I do not comprehend - in my perception, these are not alternatives for the same purpose.

Why exactly fifty-one? - and no, the wardrobe is not only too small in depth. What do the 39 cm exterior wall thickness mean, what wall construction is planned there?

The seating window is not meant to replace the counter. We simply like it. 51 cm because that is how the architect planned it.

I have to say something else about the seating window: is it comfortable to sit in front of kitchen cabinets? You don't look at the countertop, but at doors - I think the idea played a trick on you (like the 2-meter hallway…) Nobody will sit there…