Final floor plan planning - Rose-colored glasses

I agree with Pagoni - if there is the possibility of a laundry room in the basement, I would do it that way in this case. A utility room upstairs is great if it fits. Here you would gain space if the laundry moves downstairs (maybe even into a sufficiently large room where the laundry could then also be hung up).

Would that be possible?

I would still combine the bathrooms and possibly enlarge the guest toilet a bit so that there is room to move around.

what is planned when the parents-in-law no longer live there? Will you then move downstairs and rent out upstairs? Or will you stay upstairs?

I would never voluntarily put the washing machine in the basement and constantly carry the stupid laundry up and down two floors.

I would remove the sink in the kitchen at that spot and equip the entire space with floor-to-ceiling cabinets, because that fits loads of supplies, even for 4 people. This way, the pantry can be eliminated and used as a laundry room.

I wouldn’t necessarily remove the wall in the children’s bathroom area, we also had that once in an apartment, similar size, and I found it quite practical. However, we didn’t have another bathroom but only the tub/sink/washing machine room and the toilet cubicle. As usual in rental blocks, also without a window. You could then shower in the evening even if guests were in the toilet...

so I remove the fluff by hand (we always get a proper carpet out) and throw it in the trash. Sometimes the vacuum cleaner is also used. That’s how it’s explained in the manual as well. Occasionally a message appears saying that the base filter needs to be cleaned, which is located behind a flap at the bottom. That’s the only part I clean with water.

Oh, well, I also started like that. But the fluff/dust is so firmly and partially sticky in the filter that I still rinse it off after the finger carpet thing. I don’t know how my wife does it, but that’s how I always do it.

What is planned when the parents-in-law no longer live here? Will you then move downstairs and rent out upstairs? Or will you stay upstairs?

I would never voluntarily put the washing machine in the basement and constantly carry the stupid laundry up and down two floors.

I would remove the sink in the kitchen in that spot and equip the entire space with floor-to-ceiling cabinets, because then you can store plenty of supplies there, even for 4 people. This way, the pantry can be eliminated and used as a laundry room.

I wouldn't necessarily remove the wall in the children's bathroom area, we once had that in an apartment of similar size, and I found it quite practical. However, we didn't have another bathroom but only the tub/sink/washing machine room and the toilet cubicle, as is usual in rental blocks without windows. You could then shower in the evening even if someone was using the toilet...

This anticipatory planning with the parents wouldn't be that important to me given the current status quo, since the new living situation is supposed to take place first. How things will be at some point in the future would probably be more like groping in the dark because life changes are numerous; therefore, I would adjust it exclusively to the immediate needs.
Of course, there are better solutions than washing in the basement across two floors, maybe a washing machine integrated into the kitchen, and maybe it will also happen once that someone wants to shower exactly when the visitor heavily used the toilet two minutes earlier. Nevertheless, I find this somewhat dramatized because the visitor-shower-guest-toilet situation will probably never occur, and if it does, then at most 1-2 times in a lifetime. For this reason, it would be absolutely secondary to me; a guest bathroom without a window is no problem at all.
Reducing or even eliminating the pantry would be a good option depending on space in general (vacuum cleaner, paper waste, some tools, etc., nothing major but should be considered).
I would simply go by what is used often and what is used rather rarely.

that you 1. demolish a roof and 2. an upper floor, 3. then also the ceiling of the ground floor, 4. put a cantilevered new ceiling as a floor slab of a screw head penthouse on the ground floor, and 5. attach a stair tower for its access, which moreover is not even completely covered by the 6. new roof

... is still all as before, only details in the course of the interior walls have changed. It remains a Frankenstein-like treehouse that abuses and overshadows a house demolished up to the underside of the ground floor ceiling as a building ground – in other words a stillbirth (and thus I hope that the district office will prevent this folly). This has nothing to do with rose-colored glasses anymore; you would have to have eaten a magnum cup of LSD for breakfast! If I were the head of the building authority, the building application would go straight to family court for guardianship appointment of all involved. If you only look at the upper floor plan here, you might hardly understand my words – only the more exact viewers can appreciate them in view of the demolition illustrations. But anyone who looks at the whole story along with the existing house in the original thread can hardly seriously doubt the mental derangement as the seed of the crazy idea.