Optimization of floor plan for detached single-family house 155 sqm

To be able to say something about that, you first need the views and the house on the property.

Has the building application already been submitted?

In principle, too many windows are not necessarily a bad thing.

In the upper floor, however, you have floor-to-ceiling windows in the children's room, which I find very, very annoying in our case. In summer, because of the shading so that the room does not overheat, we always have to close them completely. Placing furniture - desks - is also difficult.
The staircase with 16 steps is also quite steep, maybe consider a half-turned one here; it would do the bathroom and the ground floor good.

On the ground floor, the wall on the south definitely has two windows too many. Even if the sitting window is cool, it takes up space; try placing a dining table there, which is completely missing, but please with the right dimensions.
In the utility room, which is already so small, the window also bothers, especially if the carport is there; there is not much light. I assume you want to use it as a door? Keep in mind that this is the perfect spot for a break-in.

I am also unsure about the floor-to-ceiling windows in the children's rooms. What bothers me about a parapet is that it has to be 80 cm high right away. I would also like to plan some kind of sitting window there like on the ground floor, but it wouldn’t look as nice optically without fixed glazing. We also don't have a ventilation system and therefore wanted to be able to open the window upstairs.

I can’t mentally fit a half-turned staircase into the floor plan, at least not without significant changes.

I hadn’t thought about the 16 steps yet; I will compare it with houses of acquaintances.

The sitting window on the ground floor is simultaneously a bench for the dining table, so it should fit without problems.

The door in the utility room on the ground floor is a proper secondary door with frosted glass on top. Unfortunately, it was very expensive, but in return, it is also burglar-proof.

To be able to say something about that, you first need the views and the house on the property. Has the building application already been submitted?

We have an exemption application which has already been approved.

Can you please also say where [Norden] is?

Can you please also say where north is?

The house faces north with the front door. The kitchen/living room and the children's room are therefore facing south.

I would probably reconsider half of the windows. I am a fan of windows and light. But a window has no place above a bed or bathtub. You yourself have noticed the ventilation problem. Then I see no window sills, which take up storage space. (Seating) windows should be planned and not just placed randomly in the plan. Here and there: "I'll just take one above the bed and bathtub, but then there needs to be another one for ventilation," "Then a seating window to sit at, then you immediately need a terrace window next to it." That’s not how you approach it, but it seems to have been done here. The south facade will probably look very "special" now.

Kinderzimmer:
Braucht man noch die Fenster nach Ost/West?

Yes, namely for cross-ventilation when the rooms heat up too much in summer because of the too large window fronts. That will be the case here.

Gestaltung von Schlafzimmer und Bad.

Bad:
Hier frag ich mich ob die Anordnung an sich noch verbessert werden kann mit z.B. einer T-Lösung?

First of all: the bathroom is not sensibly furnished. It can certainly be better: toilet out of the sightline, so she doesn’t need a privacy screen, double washbasin sideways next to the window, space for a wall construction and therefore more room for a mirror cabinet.
However: T is no magic. T is a means to give too large bathrooms structure or to get more installation walls.
I see another problem:
Where do you want to store everything?
Mops, brooms, batteries and spare bulbs, the quick hammer, repair paint, quick decorations, recycling rubbish, beverage crates, shopping bags... Cleaning supplies could go in the kitchen.
The freezer is already tight and will get a second door, which again swallows up space for a shelf. The wardrobe is small. Unfortunately the office can’t accommodate much either with a cupboard because there are only 50 cm behind the door. A closet for hanging jackets should be 60 deep. I also complained about this above: once spare bed covers, bed linen, and so on have to be stored, the dressing room will become tight as well.
The house is very compact. Overall, the floor area seems to me to be less than 155 sqm.
The hallway is cramped. I don’t know whether the doubly unusual staircase layout, namely 1. with the ridge and 2. towards the outer wall and not towards the hallway/center of the house, does the house any favors.
Unfortunately, the questionnaire was not filled out!