Plot for construction next to existing building - "Single-family house in Grandma's garden"

Hello dear house-building friends,

my wife and I are dealing with the desire to build a house and are currently discussing what possibilities we have.
One suggestion that is being considered comes from my wife’s grandmother: "build in my garden, there is space!".
We would like to at least follow up on this suggestion to clarify how feasible it would be / what hurdles there might be.
Since I have been reading here in the forum for some time, I would like to put this question to the group:
How well can the existing plot be developed with another single-family house, and what hurdles do you see due to the local conditions?
(Topics like modalities of parcel division etc. I would like to leave aside for the time being.)

Here are the given framework conditions:

[*]Grandmother lives alone in a small house on the plot with a double garage and a garden at the back. Her house should remain untouched.
[*]Plot is almost square, ~32m x ~32m (~1000 sqm)
[*]On the plot: grandmother’s house in the southwest of the plot, garage southeast of the center, garden/lawn in the north and west
[*]Around the plot: low-traffic street to the south, a terraced house with 5 units (and their gardens/terraces) to the east, a single-family house with gardens to the north, a multi-family house to the west (house of my parents-in-law, 3 apartments/floors)
[*]In winter, the plot has limited sun for several weeks because the hill to the south casts its shadow
[*]We are located in BW, urban area, no specific development plan
[*]The "desired" house offers space for 2 adults, 2 children, and 2 workplaces (she teacher, I IT specialist and work a lot from home)

For illustration, here is the corresponding excerpt from the cadastral map with an overlaid aerial photo (north is at the top of the plan):



Besides the described conditions, there are the following 2 "wishes":

[*]Preservation of the garden in the northern half of the plot
[*]Preservation of the double garage

As an interested layperson, and from what I have read here so far about light conditions, orientation on the plot etc., I consider #1 feasible by focusing the new building on the southeastern area of the plot.
With wish #2, however, I see a problem. To sensibly develop the southeastern part of the plot, the garage would have to be removed, as far as I understand. Or conversely: if the garage remains, I only see a very narrow strip immediately to the right side on the plan, and the problem that the garage blocks sunlight from the southwest/west. Additionally, it would presumably stand in the way of a central plot division (vertical in the picture).
The potentially lost storage space would have to be compensated - at least partially.

How do you assess the described situation? I am grateful for any input and look forward to your feedback.

Best regards
Sebastian

Have you already checked the legal side regarding the development plan, Par. 34, etc? What about the boundary construction of garages in the east? Has a distance been registered in the land register for Grandma's property there?

Draw the required minimum distances for houses on all sides. Then it will probably become clear quickly that the double garage in the middle of the property stands in the way of a sensible development.

So I actually see the only possibility for construction there as relocating the double garage. But first of all, it needs to be clarified whether any further construction is possible there at all and, if so, what is permitted. If necessary, the double garage could then be integrated into the house, but at first I don't really see a clean way to do that.

In my opinion, the best option would be to "sacrifice" the double garage, then divide the property and thus be able to build on the right part.

Perhaps one could turn the double garage into a single garage and then attach the house directly. This would leave a bit of space to the eastern property boundary.

Have you already checked the legal side regarding the development plan, Par. 34, etc?

No, we have not yet obtained any official information.

What about the boundary construction of the garages in the east? Was a distance recorded for Grandma’s property in the land register?

Do you mean the garages behind the terraced house (light grey, far right in the picture)?
We are not aware of anything regarding that.
I don’t quite understand the connection yet. How does the boundary construction with another property affect our considerations? The distances to Grandma’s property boundary are being observed.