A part of the controlled residential ventilation will also go into the utility room, so a utility room on the ground floor is indispensable
So the duplex is supposed to have four apartments, ground floor one for two people and one for one person, upper floor the same (but with access via external stairs and as maisonettes with spiral stairs to the attic), if I understand that correctly - otherwise your drawing skills are more rusty than assumed; and only your side is elaborately detailed, the brother's side, however, is almost just a volume model with the roughest layout (?)
Small town in steady growth in Münsterland. Almost no apartments available in any size. A multi-family house with a shared staircase is ruled out due to the width of the plot. Also, only 2 residential units per plot are allowed (the two plots together are only about 646m² in size). Well, nobody can guarantee that the tenant thing will work out, so far I have had few to no problems with my tenants (old house is partially rented out).Phew, it’s all quite convoluted and not very large, yet there is a lot of empty space/hallway in the middle of the ground floor apartment that cannot be used. As far as I know, controlled residential ventilation units are not so big that they need a separate room. What is the situation on site? Is there even demand for such small apartments? Why actually a semi-detached house and not just a multi-family house with a shared entrance and staircase? Have you also carefully considered whether you really want to live in your property together with tenants? Especially ones above you who practically stomp around on your head?