Floor plan, not a specific single-family house, approximately 200m² with 2 apartments

You have preconceived opinions and you don’t really want to play with floor plans, but have already fallen in love with your layout. You can tell by statements like

And, what exactly is the point of a children's toilet that would also need 2 unmarked entrances, if then for the rest you have to go into the parents’ bathroom. Better a centrally located, easily accessible bathroom for all occupants of the upper floor. Especially since the toilet drain would end up in the living room ;)

If, for example, there is only a chest of drawers in the entrance, where are coats etc. supposed to go, especially in a 4-person household with children.

For drawing... there are standardized drawing variants:
- Tall cabinets box with cross
- Wall cabinets box with a diagonal line
- Dressers etc. just a box

Stairs... a few centimeters here and a few centimeters there... here too, with your two-apartment plan, you have to remember that beds, sofas, etc. will need to be carried up the stairs. In a sketch, it’s better to plan generously than too tight.

The doors of the children's bathroom would open toward the partition wall between the two rooms.
Theoretically, the office-2 and bathroom could be swapped, but that wouldn’t only have advantages either.
Can you speak from experience (from others) that this is so disturbing (due to noise or odor) that it should definitely be avoided? It’s not like the flush is being used continuously there.

I will make sure to add the drawing variants to the floor plan.

For larger furniture, etc., on the upper floor, I have my own entrance door via the balcony.

I'm out of here ... sorry, but I cannot and do not want to understand your approaches. Especially since it is all gray theory, as there is no [Grundstück].

I'm out ... sorry, but I cannot and do not want to understand your approaches. Especially since it's all just theory, as there is no property.

Okay, no problem, thanks anyway for your comments. That's why I mentioned in advance that there is no property yet. Those who find this too "gray," as you say, are welcome to ignore the thread. However, some may still find interesting discussions or approaches to consider here.

Thanks in advance for the answer, the first one that doesn't seem like pure "destruction" to me :)

Maybe should clarify once more that it is not his/her intention with his/her post to say "you can keep it."
Just realize that a "nicer" statement among 10 "destructions" does not automatically mean: "great, go ahead."
The draft is and remains bad, even with any kind of changing rooms. Just the position of the stairs alone means the structure is not a two-family house.
There is no point in sugarcoating or making excuses here. These are thoughtless attempts.
I'm out here.

I would somehow have to test how much noise could actually be generated by it in the end.

We once had a walk-in closet with a sliding door in the bedroom, which we had custom-made by the carpenter. Because of different waking times, we thought you could quietly pick out your clothes there in the morning and get dressed after showering. But just the sliding door made noise, despite a running track on the floor and a damper at the end. It was loudest when it was pulled the last bit to make sure it was really closed. It didn’t help; you could hear everything inside the closet just as you would without it, only slightly muffled in terms of noise.
We could have better invested the money for the custom job elsewhere.

Furnish the dressing room, which, if I see it correctly, is also supposed to include the wardrobe. Consider where you stand to change and how the paths are when, for example, someone wants to go to the bathroom. Although the room is so big, it doesn't work for me. I would rather go for a well-accessible bathroom for everyone.

Regarding the bedroom play: a mattress gives way, sliding a sliding door over it will not provide a satisfactory solution. Either you have a gap when you lie on it, or the mechanism jams when you don’t lie on it, or it rattles when you turn around. The bed will eventually need to be replaced, and then the height won’t fit anymore. My conclusion would be: it maybe sounded funny as an idea, but it is impractical. Bringing in and setting up a double bed there will be demanding anyway, if possible at all. I also find the wall stub unpleasant because it squeezes like that. To interfere as little as possible, you planned a dressing room for changing, and if someone wants to sleep separately, then completely separate is surely more pleasant.

Regarding the kitchen and window: keep in mind that it doesn’t help if the window disappears behind cabinets. It is not impossible to set up a kitchen on 2.50m width; this exists in terraced houses. But you are talking about a 200 sqm dream house and have all options open, right? It is also simply a bit strange to have the narrow hallway there and then the kitchen passage parallel to it.

Please please please don’t fall too much in love with the current floor plan. I simply don’t believe that all described problems can be solved by shifting a wall by 10 cm. That probably doesn’t work structurally either. Neither the upper floor nor the ground floor feels coherent, neither as a two-apartment solution nor as one.

Regarding the topic "what happens after 10 years". Option A) one or both children stay in the house longer than expected. Option B) parents find a new hobby and are grateful for the extra space. Option C) you find a solution by then and already know what you really need in terms of space. Option D) you move again to something smaller. Option E) you try to keep a few possibilities for conversion in mind (separable staircase or similar) but don’t arrange everything according to an unforeseeable future demand. You can also simply plan smaller now if you focus on what you need now and don’t always keep in mind “if we separate that, then a kitchen could go here.”