Well, those are quite a few concerns here and there. Considering the size of the extension, I am also unsure if it is really sufficient for the seniors.
One more technical thing: I find it most elegant to place the technology in the intermediate building. BUT: As in the last draft, the cables would be built over. I am uncertain whether that is allowed or advisable. Therefore, here is the consideration to move the entrance of the extension forward:
[ATTACH alt="mit Hauswirtschaftsraum.jpg" type="full"]38999[/ATTACH]
This opens up the chance for a small utility room. Additionally, the bedroom door can be relocated and the space for the wardrobe can be increased.
The bathroom is a concern. Although it is sufficiently large for such a small apartment, is it the same for the seniors? You could now shift the bedroom and hallway back and forth until the supposed optimum is reached everywhere. But if I compare it to the parents’ paradise next door, it is practically a shack.
The question, of course, is also how flexible the prefab house providers are? (Who are they anyway, can someone suggest a name?) Also, in my opinion, you urgently need to talk to a specialist (e.g., construction manager or similar) about the technology before falling in love with any contingencies.