Floor plan assistance: 216 sqm single-family house with granny flat & double garage

Or one realizes that the house simply cannot be made suitable.

Suitable for what or for whom? I’m afraid you are relying too much on your own ideas.

Yes, I admit, I like my kitchen close to my living room and don't like sloping ceilings. Plus, I consider open spaces the dumbest form of living space destruction in a typical single-family home, which you have to be able to afford. As a trick to connect a kitchen-living area with the upper floor, I find an open space unsuitable. It doesn't create a good flow. Open space to the attic - I am definitely on board with that. But destroying about 30 sqm of high-quality living space for air? With all the problems it brings for acoustics and window cleaning? Nope. And I know how many glasses, bottles, dishes you carry back and forth between kitchen and living area thanks to children. Maybe a bit less in summer, but in any lousy weather. And yes, the seven-year-old is especially good at hoarding plates and bottles in his room. I'd rather not carry that up and down two floors. :) So, you should carefully check whether you are the type of person who eats every meal and drinks every beverage sitting at the kitchen table or more of a couch lounger.

In our living room, no eating is allowed. Whoever snacks must clean it up. This also applies to an open-plan room. You don't really think there will be new [Pombären] in the living area or children's room if the old bowl is still there, do you?

I consider the house unsuitable for the needs of a family with 1 or 2 children

Good morning everyone,
Feedback from the architect:
…it would be necessary to move the wall in the upper floor living room to the garage wall, and to move the wall between the staircase and the work area to the wall below in the ground floor toilet. The windows facing the garden would need to be arranged so that I can run a beam under the ceiling over the upper floor in the area of the void from the wall between the staircase and the work area, and the support would run on the garden side from the attic down to the ground floor.
Then it should work.

Do I understand correctly that a beam would have to run across the void from one long side to the other long side of the house??
Right now I don’t know whether to cry or laugh :/

I consider the house unsuitable for the needs of a family with 1 or 2 children

Well, that is already criticism at a high level. What are the mothers supposed to say in the apartment building on the 4th floor with a washing machine in the basement? For small children it may not be as practical as a detached house from the drawing board. But they do grow up eventually. We ourselves have a house in the family where a similar constellation exists. Kitchen / dining on the ground floor, living on the upper floor, sleeping in the attic. I can't say that it bothers me. Especially in summer, you are almost only downstairs.