Final floor plan planning - Rose-colored glasses

Go through the entire process of "doing laundry," and you'll realize that it doesn't work like that.

It's not just about throwing the dirty laundry into the washing machine and taking it out again.

Laundry is collected, and I especially think of my husband's sports socks, which definitely can smell when dirty. Are you supposed to present that scent to the customer?
In summer, you can hang laundry outside. What do you do in winter? Or when it rains? Carry the wet laundry into the apartment?

Where do you iron?

I don't see a sink in the office (which I like!), so what do you do with the condensate from the dryer? Carry it through the hallway into the guest bathroom, which is so small that it will probably be difficult to empty the container into the sink?

Laundry is not only collected but also sorted. At least I have whites, darks, towels, etc. for 60°, boiling wash. Well, you have a collector in the office, but where should the other piles go once the dirty laundry has been sorted for the wash? At my place, the sorted piles lie on the floor waiting to be put in the washing machine, but that will hardly be possible if the room is also used as an office.

I would reduce the office size a bit and add the gained square meters to the bathroom or children's bathroom (the entire children's bathroom, without the partition wall to the WC, which has already been pointed out) and place the washing machine and dryer there.

In the office, that is absolute nonsense.

Furthermore, I don’t find either bathroom very impressive. A second or children’s bathroom is nice if you have the space. Here it would be too tight for me. Furthermore, the children’s bathroom doesn’t even have a window.

Keep the guest toilet and merge the children’s bathroom with the master bathroom – so only one bathroom. Add a few square meters from the office, then it becomes a nice, large bathroom with enough space for a utility room corner with a washer and dryer, and then there is also a sink nearby.

I don’t know what the gray and red walls mean. Is one load-bearing and the other not? Did I miss something?

You should give up the dream of your own parents’ area given the spatial conditions.

Are you even getting approval for the renovation?
Why don’t you, for example, put the office downstairs so that the floor areas can be planned more evenly?
I think this mini children’s bathroom is just a wet cell. Something has to go in there for which there is no space.
Why isn’t it being renovated and converted the way many others do?
The term treehouse fits quite well

I was at a bathroom exhibitor yesterday and he said that the size was completely adequate and that I shouldn't worry about it.

I’m by no means a floor plan expert, but to me it looks a bit angular, more like the much-described Tetris.
Depending on what your husband plans to do in the office, but with customers there, a bathroom should also be accessible from there; the one with washing machines etc. has already been mentioned and would be an absolute no-go for me because of heat, the feeling of living, and noise. Is there no basement or communal room in the house, like in a typical condominium? Also, I would combine the two tiny bathrooms into one, even though I basically like the idea of a separate guest WC.

That probably only works in theory; imagining it in practice, I have to rather smile when I think of some emerging situations.

Guests in the guest WC are rare, the tiny bathroom for you is always used. I wouldn’t do it that way.
I don’t have a direct idea right now, but rather I would steal about 2 sqm from the pantry and make a guest WC out of it, since with floor-to-ceiling shelves you can easily have a pantry on 2 sqm that secures your food for months (we have less than 2 sqm here, so I see it).
As I said, some things also depend on whether there are basement rooms or similar.