@ The bidet is supposed to go into the family bathroom because it is not needed in the master bathroom.
If you want more ideas, suggestions, and critiques, you should clarify what purpose the master bathroom and the communal bathroom are supposed to serve. Because obviously it deviates from average usage.
Is there a rule that the guest WC has to be smaller than other bathrooms?
Just logic in space allocation. If it makes sense to you this way – build it like that.
Why shouldn’t you be able to transport 3/3 of the laundry through the chute? I understand that the detour via the kitchen is not ideal, but we can live with it.
Because not all of the laundry originates in the master area...
That was an example; I can well imagine simply adding a 2m bench with hooks for jackets, since you don’t really do more than put on shoes and jackets there.
That can definitely be done. But then you have to plan that all change jackets, seasonal shoes, scarf-hat-gloves, sports shoes and so on need to be stored somewhere else. So space must be allocated in the dressing room, attic, or wherever it is supposed to go. Because nowadays it is usually the homeowners’ wish not to store all this in the wardrobe, attic or such, but rather in the cloakroom.