Floor plan of a two-family house (side by side) on a south slope

I can't really judge as a layman and it is not very relevant to me whether this is a Leistungsphase 1 or Leistungsphase 2 drawing, right?

Right. In Leistungsphase 1 there are no drawings yet, and in Leistungsphase 2 they should not be detailed yet. Planners who "ramp up" too early are dangerous (usually inexperienced and poor budget watchers).

Or. In design phase 1 there are no drawings yet, and in design phase 2 they should not be detailed yet. Planners who "ramp up" too early are dangerous (usually also inexperienced and poor budget controllers).

Thank you for sharing your experiences and concerns. We have a good feeling about him; he is not inexperienced since he planned the first house of the older generation 35 years ago. Would you maybe also like to evaluate the floor plan and changes?

My idea is to shorten the house by about 1m in the north-south direction.

Basically, you should reduce the size of a house design if it is too large.

Basically, we like it very much,

To be able to say that, you should use the design to draw in real or already existing furniture to scale in order to recognize any shortcomings and overhangs. For example, I consider the kitchen's size to be absurd, just like the access to the storage room or the airlock function of the storage area. You should be aware whether you want to follow the trend of having a kitchen with no space, only a pantry instead.
Whether you actually want the guest toilet there as it is - I mean, who is supposed to use it? Those coming home will go upstairs faster. The guests surely do not want to be so close to the table. And whether the few sleeping guests really need to shower in the main bathroom is also a question.

On the ground floor on the right about 0.5m in the home office and in the living room at the TV wall, on the left in the technical room.

Does the home office even serve guests anymore? I rather see potential in the living room... if at all. Because the 9.23 should be realistically divided, as already mentioned.

On the upper floor on the right divided between child 2 and parents, on the left utility room and bathroom.

Here, too, I see a very large overhang in the bedroom. Aside from that, you cannot simply approach the rest as a reduction/shortening also affects the doors.
So before simply cutting it short, I would check what is visible in the design if I were you.

Thank you for the comments.

I think I would also move the door to the pantry/storage room to the hallway.

We need to think about the size of the kitchen and the location of the WC. The shower can probably be omitted.

The home office is mainly intended to serve as such, but there is consideration of placing a sleeper sofa there - but that might be worth reconsidering.

You are right about the doors; that no longer works with a reduced bathroom.

Would you also like to evaluate the floor plan and changes?

That would probably be a waste of time. You said you still wanted to shrink the shown part, and in the part not yet shown the modifications would be even more extensive. In other words: the shown part is scrap that we are supposed to mentally reduce by the width of the house, and the not yet shown part is an even darker black box. So basically everything I could "evaluate" is missing.

You said you still wanted to shrink the part shown, and the revisions in the part not yet shown would be even more extensive.

I think so too: a different draft will result, and whether this one is now considered good, I do not see for the reasons mentioned.