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

You can easily deal with the topic of privacy with a partition wall

I don't really think that's a good idea. We lived wonderfully together with the parents in one house for many years and I would do it that way again. Nevertheless, I would handle some things differently, such as no shared entrance, outdoor areas on separate sides of the house. People change, your feelings do too, and so you CAN meet every day and for a long time, but you DON'T have to. No one! I would consider that a gain for both sides. It was important to me that they have a stylish apartment and that you can also "visit" each other there. A partition wall does separate... and yet it doesn't. You can hear... and in my opinion it’s too close. The parents might be hard of hearing and have loud music or phone calls. I really like living together, but a clear separation is indispensable for me.

.. mh - well, the parents will not live forever; if you then want to rent out their part of the house, you will also have those people integrated into the family. I would think about that carefully again…

That is an important point, so divisibility or separability would be important to me. Maybe later one will move into the smaller apartment oneself or... I would therefore plan it as if you were "strangers", you can still come together anytime. And... living together desperately needs clear and discussed rules, suppressed wishes and ideas often lead to gallbladder complaints. As they say: The worst thing is always to say everything right from the start - both sides!

Regarding the architect and without a real limit ;)
Look for Fabrinsky; he's in your region and as you can see, he has even built on a hill before. But I fear he can’t do a hip roof. Anyway, I would first get a suitable architect, then you will get a house that looks exactly different than the one currently in your head. :D

The driveway is about 100m long depending on where you measure it, approximately 3.5m wide, has a 90° turn and overcomes just under 11 meters of elevation. [...] Parcel services now come up, as you can turn around at the top if you want to.

"If you want to," haha. As if anyone would enjoy maneuvering backward over 11 meters of elevation *LOL*

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I don't really think that's good. We lived wonderfully for many years with the parents in one house and I would do it that way again. Still, I would do some things differently, like no shared front door, outdoor area on separate sides of the house.

...therefore I would plan it as if you were "strangers," you can still come together anytime.

...

Regarding the architect and without a real limit;)
Just look up Fabrinsky;

Maybe I expressed myself wrongly or not completely—the parents will have a little table on their side and we will have one for ourselves. In the middle, we imagine a come-together area. Maybe we will separate both halves with a small outdoor kitchen around the gas grill.

We will take your advice to heart. Especially the "plan as if you were strangers" has some truth. We don’t have a shared front door, unless you also mean that they are next to each other—which won't be avoidable.

I’d pay Fabrinsky 150k immediately if he saves me 150k ... so that way I’d have the planning for free.

Seriously now, I would really appreciate finally finding someone capable. Even if it’s just someone who says “that’s not possible, you have to make compromises, it will cost this much.”

Seriously now, I would really appreciate finally finding someone capable. Preferably just someone who says “that’s not possible, compromises will have to be made, that’s how much it will cost”

We’re probably all looking for that.... you’ll probably have to make a decision then.

Maybe I expressed myself incorrectly or incompletely

No, I think I understood you. As I said, we lived it like that and I would do it again, so I’m not painting a horror scenario for you but rather want to encourage you. I experienced it as something absolutely positive! Still, every person, even if it’s only later on, has the need for peace and does not always want to feel watched. Even if you’re not even being watched, just the possibility can already be disturbing. By the way, I always think of it as 50:50, because even the older folks might sometimes prefer to be alone but would never say so. The thing with the building entrance was just meant as an idea, because sometimes you just do your thing alone and don’t always want to be asked. We had a shared stairwell and I’m still alive. Generally, I think it’s more appropriate if each side really has a separate area. You might also want to grill or do something else without visitors. There are probably several other reasons I would have to think about but I know that I would definitely find it more appropriate FOR BOTH sides if it’s separated. Saying no is very hard afterward and can also sometimes be misunderstood by the other. Does Farbrinsky really cost 150? In the end, it’s the overall project that matters. It’s easy to hide five-figure sums quickly for things that later turn out to be nonsense; a capable architect definitely has its justification!

No, I think I understood you. As I said, we lived it that way and I would do it again, so I am not painting any horror scenarios on the wall for you but rather want to encourage you to do it. I experienced it as something absolutely positive! Does Farbrinsky really cost 150? Ultimately, the overall project is what matters. It’s easy to hide five-figure sums for things that later prove to be nonsense, a capable architect certainly has its justification!

You are absolutely right there. How we can solve the access problem without having to walk around the whole house or abseil down the northern neighbors, bring on your ideas. No idea what Mr. Fabrinsky charges as a fee. The fact is, the architect needs to be experienced and pay off ‍♂️ I once asked the surveyor Mr. Hell from Öhringen to take care of the property. Additionally, there is the surveying of the extra plot and a soil report ... then we can start planning the house. Then we’ll also see how big it will be, where and how it will stand and thus how much earth needs to be moved. Another consideration is to place the house further south to have more shaded garden on the north in midsummer. Tomorrow I will call some architects that I will find tonight.

Another consideration is to place the house further south to have more shaded garden to the north in the height of summer.

That is definitely worth considering, especially since sun/light will also quickly come over the roof due to the steep slope.

Regarding Fabrinsky: the projects are too unfriendly to nature for me. I would aim for something more organic.