Setback areas 2. Garage State Building Code Baden-Württemberg

Look in your state building code Par. 5... Garages are privileged for boundary construction.
Regarding the lower properties: that might perhaps be special usage, if the workshop was also built that large. Often, setback areas are taken over from the neighbor. But that costs land registry entries. Here, the adjoining of the garages may still play a role, so that one could utilize 12 meters with the neighbor's consent. They do shake hands after all. Warning: layman's opinion!

Basically, you are allowed to place 25m2 on the boundary. Par. 6 Landesbauordnung
If these are "used up," Par. 5 Landesbauordnung applies regularly for the rest.

In my opinion, the 25m2 are also not divisible. Meaning 2 buildings of 10m2 each.
For older buildings that were previously, often illegally, constructed, there is often a vested right. Which does not mean that you are allowed to build like that again.

Just ask the building authority. If it's not too complex, you will get the answer by phone.

Edit: Especially since your plan touches two boundaries. That is also not allowed. 25m2 may only be used once :)

Yes, I have now asked the building authority for an appointment. If anyone is interested, I can report back later. I would have just liked to know exactly beforehand before contacting the authority.