Single-family house with a ground-level granny flat on a slope

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I prefer to stick to water and wine.

That’s not bad and was already practiced about 2,000 years ago in the eastern Mediterranean region, among others, by a certain group of people :)
There was even supposedly someone who could turn water into wine ... ;)

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(stoning
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That was also popular at that time ...

Water and stones aside, although both of course also have something to do with house construction :) since the interest in my post is very low, here again the question: can you name me a hangerexperienced planner who is within the 74(6) area?

The plan is a 2-story single-family house (140 - 160m2) with an attached bungalow for the parents (80m2), so a total of about 220 - 240m2.

I would probably push the building for the parents forward a bit (i.e. into the slope) and then put a level from you on top, so that a corner is created at the front and it is a bit more open. Otherwise, you sit on your terrace and look again at a multi-family house appearance.

Thank you, we had the same thought at first, but the wife and mother-in-law prefer it differently (although both say they need to see it first to decide).

Do you happen to know if a precast solid basement is just as load-bearing as a solidly built basement?

Would it be daring to make the terrace/balcony at the back a bit larger so that a) there is more space at the top and b) a roof is created underneath? Additionally, I imagine a staircase directly into the garden. Is the balcony planned to run all around the house, meaning two sides of the house?

I believe there is a misunderstanding regarding the basement wall: the statement was that if you have a basement in a hillside, the house built on top should preferably be made of masonry to create a higher weight that stabilizes the basement wall on the hillside side. It can be done differently (for example, we have a rather daring construction with a masonry basement with earth pressure beams and a timber frame building on top), but it makes sense. In your case, a concrete basement is more suitable (so also a precast basement!).

Your problem right now is the other side of the house, namely the valley-side access. Once that is resolved, the basement will be a breeze.