Single-family house with barrier-free granny flat on the ground floor

After the residents of the granny flat have passed 80 - do you think they are still fit enough to live alone after the construction? I see how quickly my seniors are currently declining. I would no longer plan and build an apartment for all 5 - rather a nursing home

I see it differently.
Of course, one does not know how things will develop. My mother-in-law is now 90 and we are currently dealing with the topic of nursing homes or nursing shared apartments. That is not a given, and finding a really nice one still nearby that also has available places is even less easy.
We would have liked to include her here in the new building when she was 86 and planned it accordingly, but she absolutely did not want to live with any of the children, but wanted to live independently all her life. Today she would probably see that differently, but that’s how she wanted it.
My mother had five sisters and all of them are cared for in very different ways and supported by their children (with the help of external assistance/care). These children (some of whom are today already partly up to 80 years old) all had professions and their own children etc., but due to their tradition it would have been hard to imagine placing the parents in a home. In that respect, I also see, regardless of age, both possibilities or the necessity to clarify that individually. Of course, that also has its limits, I am well aware of that from my own experience, but I believe there are many possibilities in between if one wants that.
I don’t want to judge it, but only to show that it would often be possible.

I think I have the whole range and have been rotating for 12 years so that everyone can stay in their own homes. There comes a point when it no longer works. Especially currently, it is shifting from spry to we probably need a caregiver.

A 24-hour staff pushes the point of it no longer working far into the future - there is no room for one.
There is also no direct connecting door planned to quickly check at night or give the senior their food or put on their socks.

I understand that, and we have also been involved in that in various ways. I think there are so many and very individual situations that you can never cover with blanket ideas, which you sometimes read. We are currently dealing with this with the mother-in-law.

and have been rotating for 12 years

And of course, eventually you get tired of it. From time to time we are in small facilities and make some music for the people there, and there we have indeed met people who should/would not yet have to be there. Of course, it can also be that the OP builds the thing and three weeks later some circumstances change, but there can also be 10 beautiful, shared years ahead. Basically, I find it nice when someone does it today and does not immediately always show the filing box with explanations against it. In my close circle I know two families where the elderly have cleared out their house for the younger ones or moved into the small apartment. When I asked if they would also take care of the elderly, they just shrugged their shoulders in a startled way and explained to me in a similar manner that they basically have no capacity for it. Certainly not the normal case but still sad. As I said, I am not talking about full-time care. Well, let's see what comes from the OP.

How many people of which age are moving into the [Einliegerwohnung]?

Before I respond to the first comment from , a brief note that I do not want to discuss the sensibility of a newly built granny flat for over 80-year-olds or the budget here. Yes, both can be questioned, but my primary focus HERE is on the floor plan design.

So, I will address the first comment from point by point (without the comment function), hoping I haven’t forgotten anything. Let’s start with the granny flat and garage

[*]The garage is currently still optional, but we are already making many compromises because of the granny flat, so I don’t want to give up on a single garage. Otherwise, it probably would have been a double garage
[*]In the first draft, the entrance to the granny flat was at the front of the house, but we really didn’t like the layout. However, we are open to drawn ideas
[*]The conflicting doors of course must not remain like that, honestly, I hadn’t really noticed before
[*]Corner entry shower is really unpleasant, we will also have it planned towards a walk-in shower
[*]Well, the door madness wasn’t my idea but my parents’ wish. Each room separated and with a window. Maybe you can work with lightweight walls to make it more flexible to adjust "later." I would keep it completely open; maybe the vestibule would remain

And now off to the main apartment:

[*]Shower on the ground floor is out of the question
[*]En suite bathroom maybe only if it remains accessible to the children without having to walk through our bedroom
[*]Good point regarding the size of the dressing room, we need to look at that more closely
[*]We both really like the T-bath and it should definitely stay
[*]Regarding the roof terrace, all I can say is: Yeah, we’ll scrap it. I only mentioned it as an idea, but actually more for the future in case the kids are interested. At least a small exit should lead there so that laundry can possibly be dried in the summer.

How many people of what age are moving into the granny flat?

2xÜ80

Garden shed in the southwest, if at all it will be moved to the northwest for garden tools and bicycles

in the driveway?

En suite bathroom possibly only if it remains accessible for the children without having to walk through our bedroom

probably means by en suite bathroom the small master shower bathroom, while the large family bathroom is accessible to everyone and rather used by the kids.

but my main concern HERE is the floor plan design.

The house design and floor plan ultimately depend on the budget. Therefore, please understand that speculative ideas are rarely commented on if they will never be built anyway.
I will therefore only roughly address some comments or passages. First of all: the type of house is nice. It looks as the architect visualized it, with a fairly pleasant impression, although the entrances do not exactly welcome you, they rather modestly hide away.

open or closed architecture: rather open (open galleries are not meant here)
conservative or modern construction: yes
open kitchen, kitchen island: 2x yes

We saw it like this in a show house and immediately agreed it should look like that.

Living/dining/cooking – every second house has this L-shape. The layout is conventional and therefore suitable.
An open all-purpose room is present; whether that is a defining feature of modernity, I don’t know. For that, I miss a visual axis from the entrance toward the garden and something other than a U-shaped kitchen. The kitchen is somewhat petty. I would take something away from the pantry/backup. Because a kitchen that doesn't work just to have a backup kitchen is nonsense.
I personally find the T-solution boring, this roof terrace questionable as to its purpose if you have to maintain the garden.
The walk-in closet I find uninviting.

The part around the stairwell, door to the technical room and guest WC somehow feels cramped/unharmonious

No, that will work. Yes, WC in the dirty area, yes, very narrow. But you can't fit a stroller, and if necessary, you put on and take off your raincoat in the kitchen; what’s the big deal.
If you take a bit from the backup kitchen sideways, it could be more spacious.

We actually like the straight staircase but it is completely hidden so that you basically only see the stairwell

An open staircase must be clearly defined for an architect, because an open staircase is planned differently. It also results in a different house.

Which wishes were implemented by the architect?
Primarily based on our wishes. These were largely implemented, but especially the arrangement/implementation with technical room, stairs, pantry bothers us a lot, at least on paper,

It also appears that you want more. Everything is fulfilled, and then you come with unimportant things that were seen somewhere, and then you want those too, and then that, and then something else. Humans are greedy: when they get what they want, they ask for more.
You have to stay grounded: budget, wishes, limits.

Since the house plan is quite usable, here are some tips:
Definitely draw your own furniture to scale. That is what the design is for! Whoever does not take the time for this will have a rude awakening later.
The attic expansion will not be usable as drawn with the height specifications. You can't have a desk with a PC there, etc.
The cupboard by the stairs won't be accessible at all. I would remove the wall there and then install sliding door elements. Then it’s an extra-deep closet, and that is super useful.

I find a granny flat complicated. It becomes quite tight for two people. You get in each other's way. The same applies here: definitely check daily routines. And which furniture is needed? They might rather want to put a wardrobe near the table instead of the 98" TV?