Floor plan design of a semi-detached house for 1 family (4 persons) on a small plot

Hello,
we will be building next year, have found and purchased a small plot of land, and already have a house provider (still waiting for funding, so nothing is moving forward at the moment) - regarding the planning, the "preliminary planning" by the construction advisor from the prefab house provider is, in my opinion, only a suggestion and still far from optimal, so I hope to benefit from the collective knowledge and experiences here in the forum. I have attached the floor plans (anonymized) as images.

My core topics right now are the following:
How do we distribute the children's and parents' bedrooms?
Where do we put the study?
How do we get two nice bathrooms in a small space, one focused on the children, one more for us?
What alternatives are there for the cooking-living-dining area, possibly also not open?

Here is more information:

Development plan/restrictions
Plot size: 270 m² - 27x10 m
Slope: no, but embankment, the street is about 1.4 m higher than the rest of the plot.
Floor area ratio: 0.4
Building window, building line and boundary: 12x10 m building window, 3 m from the street, sketch attached
Edge development mandatory, as it is a semi-detached house (see plan)
Number of parking spaces: 2
Number of storeys: 2.5 (2 full storeys are required, 6.5 m eaves height is also binding, as is a maximum total building height of 10 m (measured from street level)
Roof shape: 35° gable roof
Style: classic?
Orientation: north-south
Maximum heights/limits: see above, max 10 m, exactly 6.5 m eaves height

Requirements of the builders
Basement, floors: Due to the embankment and small lot size, we want a utility basement; we want to develop the attic (now or later)
Number of persons, ages: 2 adults, late 30s, 2 children (0 and 3)
Room requirements on ground and upper floor: Basement: laundry and utility room, hobby room, possibly with an outdoor staircase; ground floor: living, dining, kitchen, guest WC, possibly study; upper floor: 2 children's rooms (preferably 14-15 m²), bathroom, possibly study or guest room or parents' bedroom (I consider this too tight, but open to suggestions!), attic: additional bathroom (unclear whether the bathtub should be in the upper floor or attic), parents' bedroom, possibly study (we don't actually need a huge bedroom, hence the considerations. Due to the age of the children, we would prefer to live with them on one floor, but I can't find a nice layout that accommodates the three bedrooms and one bathroom)
Office: family use or home office? Home office absolutely necessary, at least a small one
Open or closed architecture can be open, but for example, despite an open living-cooking-dining area, we want the staircase separated to avoid possible noise (e.g., from children) or odor nuisances. But we are open to suggestions!
Conservative or modern building style: I think rather modern but simple
Open kitchen, kitchen island: gladly open kitchen, we thought of an L-shape with a small counter. We like cooking a lot, so this would be an important place
Number of dining seats: 6-8 seats, one dining table. If kitchen and living-dining room should be separated, then probably a 2nd dining area in the kitchen
Fireplace: no
Music/stereo wall: not needed
Balcony, roof terrace: no
Garage, carport: carport planned, possibly with storage room
Utility garden, greenhouse: not planned

Further wishes/special features/daily routine, also reasons why this or that should not be:
Since the second child is still unborn, we are not 100% sure about the daily routine yet; currently we live in a 4-room apartment. We would actually like to have all bedrooms on one floor (probably we could move then, i.e., live in one level for the first years and then move to the attic?!), my wife definitely wants a WC or better a shower bathroom on the floor where we sleep. We spend a lot of time in the kitchen or dining room, actually don’t sit on the sofa very often; the cooking-dining area feels more central to us than the sofa.
I often work from home, so this definitely needs to be more than just a small closet, but only requires a desk and some storage for folders etc. It should also offer the possibility to withdraw (e.g., also work on the PC in the evening or so); my wife also sometimes works from home (teacher), so two desks would be great, but we know it will be tight.

House design
Who is the planner: house seller/"planner" prefab house company
What is particularly liked? Why?: the fairly large children’s rooms, because they are more important to us than the parents' bedroom (just bed and wardrobe needed there),
an office with sufficient lighting so that work is somewhat enjoyable,
many windows (especially on the ground floor), hopefully enough light as a result.
Lots of space on the ground floor because much of our family life will probably take place there in the coming years.
What is not liked? Why?:
The "large" bathroom on the upper floor if we live in the attic and actually want the coziness of the bathtub, which the children will probably not care much about..
The attic window on the south side should go, so the bathroom should also move to the north side - the south side is supposed to be completely covered with photovoltaic panels. Currently, because of the position of the stairs, everything would be shifted, I lack the understanding of what the rooms could look like afterward or how to solve this otherwise.
Possibly the office upstairs if the children might be loud and I have appointments..
The feeling that the spacious ground floor wastes space and might not provide retreat areas or anything else.

Price estimate according to architect/planner: approx. 415,000 euros
Personal price limit for the house including equipment: approx. 425,000 euros
Preferred heating technology: heat pump, air-air, indoor installation, underfloor heating

If you have to do without, on which details/extras
-you can do without: guest room, significantly larger bathroom, huge office, huge parents' bedroom
-you cannot do without: two children’s rooms with at least approx. 14 m², two showers or bathtubs in total, guest WC

Why is the design the way it is now?
Strongly based on the standard with a few wishes, such as the larger children’s rooms. However, overall, there has not yet been any real consideration of what makes sense and how to do it so that it also feels good to live there.

That reminds me of Goalkeeper, the thread is overall worth reading, also because of problems that can occur with the second builder:

425,000 euros for the house including the basement seems ambitious to me.

For Goalkeeper, I once made a design that planned the technology in the attic, the parking spaces diagonally next to each other in front of the house. For that, on the right side of the house at the boundary, a kind of garden shed with a lockable annex for the bicycles.

That might make the garden behind the house a bit smaller, but then fully usable. And a well-accessible place for bicycles should be planned. For that, the kitchen is nicely located directly at the garden, and the living area is more of a retreat for TV/reading, etc.

Entrance from the side ... here simply the pictures without further comment.

[ATTACH width="347px" alt="grundrissplanung-doppelhaushaelfte-fuer-1-familie-4-personen-auf-kleinem-grundstueck-667340-1.png"]87020[/ATTACH]
[ATTACH width="345px" alt="grundrissplanung-doppelhaushaelfte-fuer-1-familie-4-personen-auf-kleinem-grundstueck-667340-2.png"]87021[/ATTACH]
[ATTACH width="347px" alt="grundrissplanung-doppelhaushaelfte-fuer-1-familie-4-personen-auf-kleinem-grundstueck-667340-3.png"]87022[/ATTACH]
[ATTACH alt="grundrissplanung-doppelhaushaelfte-fuer-1-familie-4-personen-auf-kleinem-grundstueck-667340-4.png"]87023[/ATTACH]
[ATTACH width="342px" alt="grundrissplanung-doppelhaushaelfte-fuer-1-familie-4-personen-auf-kleinem-grundstueck-667340-5.png"]87024[/ATTACH]

Is the other semi-detached house Bauer already there?

The attic window on the south side should be removed, so the bathroom should also be moved to the north side

Moving the bathroom to the top of the plan makes sense because toilets all drain through the roof, so it is more practical to plan them stacked one above the other; also, nobody wants the waste pipe in the living room on the ground floor.

Position of the stairs shifted the whole thing,

There is hardly any leeway here! Because of the heights of the roof. I would leave them there and adjust the bathroom accordingly.

no retreat spaces

How many do you need? You have the attic floor for yourselves, right? However, I would swap the living room with the kitchen. Make the toilet narrower, move the wardrobe to the left of the plan, and design that room as a retreat area. The kitchen would then be by the terrace, thus separating the living area from the quiet area.

The relocation of the bathroom to the top of the plan makes sense because toilets drain over the roof

You don't really mean that, do you? Or is that autocorrect? More likely vent.

The budget is extremely tight and, in my opinion, does not match your desires. You can also tell this because the planner is already just barely under your maximum, and they tend to underestimate. According to my calculations, it’s just enough for 2 floors and a basement. The roof is going to be quite thin. If I see it correctly, you could actually build 7x12 but the money only allows 7x10, right? Unfortunately, that is not very encouraging. Under these circumstances, I also don’t see a 15 sqm children's room. The sketches clearly show that there is hardly any space left to take away for the children. However, I find 13 sqm for children absolutely okay. Overall, I fear that you will have to lower your demands a bit or increase the budget.