Final floor plan planning - Rose-colored glasses

have you considered actually taking the children's bathroom, the toilet, and the planned wardrobe as one room. You could then install a window to the hallway (next to the office) and at least wouldn't have a pitch-dark "bathroom"

the living-dining-kitchen area is quite large at 51 sqm, you could push the kitchen wall inwards a bit and then have a wardrobe area.

not a bad idea. What do you think if I combine the children's bathroom and toilet into one room with a washbasin, shower, and washing machine? And for that, take some space from the office to create a more spacious guest toilet?

Is used by my mother-in-law.

.....hm.....whatever may lie behind these words-. I understand that you are not a fan of it but I wouldn’t be a fan of a micro-shower and an office with mandatory washing machines and other restrictions either....better to go to the basement now and then, where you go more often anyway, because you have to go to the front door on the ground floor anyway. If the shared use of the laundry room with "mother-in-law" is already not the first choice, how will it be with all the other things of living together....- . There are changes in life......where for mother-in-law maybe completely different things will be. There are separations, sad changes......and you want YOUR OWN SELF-DETERMINED living for yourself. That’s exactly what you are paying your installments for. The life of the son may always change, he is just the boy....the daughter-in-law too......??? Oh dear......fingers crossed. Is there really a "problem" with the mother-in-law’s laundry room??

then I would rather put the guest toilet where the children's bathroom is now, make the guest toilet and the wardrobe into the children's bathroom, and then carve out the space for the washing machine / dryer from the office and integrate it into the bathroom.

Then you would also get rid of the built-in dilemma of the equipment in the office....

Personally, I find a bathroom without a toilet somewhat suboptimal... (or you separate it with a sliding door)

in general: think twice about living under one roof with the parents/in-laws. Both my boyfriend (ex in-laws) and I (my parents) have not had such good experiences. They really interfere in EVERYTHING.

My boyfriend said he would have had to try to finance it alone back then. The "price/performance ratio" of bringing the in-laws into the house definitely was not worth it....

in general: think twice about wanting to live under one roof with the parents/in-laws. Both my boyfriend (ex in-laws) and I (my parents) didn’t have such good experiences. They really interfere in EVERYTHING.

My boyfriend said he had to try to finance it alone back then. The "price/performance ratio" of bringing the in-laws into the house definitely did not pay off....

It can be great but also terrible.
I voluntarily did it for about 30 years and would do it again, as everyone "benefited", especially those with children.
Still, it is basically more the case that you stand in the second row as a daughter-in-law, even if you are liked; it is absolutely human that your own son is closer to you.
I left it up to my wife whether we would do it this way or differently, and she gladly wanted it this way; I would have also done something on my own.
You MUST agree firmly beforehand and clearly express that you want to remain independent and act as you want yourself. You must not mince words, not even with mother-in-law or father-in-law.
The most important thing, however (which unfortunately is often the actual problem), is that your husband (the boy in the house) is 101% loyal to you!!! Even if it occasionally has to go "against" his own mother, he must be on your side (not blindly but loyally!).
If this is not guaranteed 101%, this healthy distance and freedom, there will definitely be problems which then will be solely to your disadvantage. For me it was really wonderful but without this attitude it would have been tense. In addition, my parents would never have interfered by nature.
If you cannot answer that with 101% YES, your tiny bathroom or alpine style will eventually be your lesser problem.
So if YES – then it is absolutely great
If not quite sure – despite the already advanced inner planning it is no problem to decide on something else for YOUR family.
Big difference: We partially rebuilt with the parents’ money and created a nice attic apartment for them. In their own house you will probably always play second fiddle. The problem and also the solution is solely your husband and his attitude!

I liked living under the same roof with my parents. I could also imagine it well with [Schwiegereltern]. I only care that the OP and her husband don't get any interpersonal problems. Father had a hard time fighting for every nail that had to go into the wall.

then I would rather put the guest WC where the children's bathroom is now, make the guest WC and the wardrobe into the children's bathroom, and then carve out the space for the washing machine / dryer from the office and integrate it into the bathroom.

Then you would also get rid of the built-in dilemma of the appliances in the office....

Personally, I find a bathroom without a toilet somewhat suboptimal... (or you can separate it with a sliding door)

I have now tried a little to change the plan myself graphically. What do you think? I also think the wardrobe would not be lost then.
Otherwise, I wouldn't know where to put it.