How many residential units are possible?

The plot measures 19m x 31m (width x length). If I mentally deduct 6m distance on one side and 3m distance on the other side, the potential house can still have a width of 10 meters. That should be enough for a standard 130-160sqm house, right?

That should be enough for a standard 130-160sqm house, right?

Why do you want to build "closer"?

That's a secret ;) .. there are also no site plans or references to the applicable development plan or anything, which would be helpful for sensibly answering the questions.

On both sides, the distances each apply.
If it were three meters (in Hesse, 0.4x wall height = wall height (formulated as eaves height), so at 7m height it is only 2.8m), these apply on the second house both on the right and left. Whereas for the first house this distance area is no longer privileged and therefore no garage may be built there – on the other side, however, it is allowed.
Whether you also have to consider fire protection issues due to boundary construction or anything to do with the development plan or other matters needs to be checked.

Why would one come up with such an idea? Does the first house really need so much space on one side of the property? Without serious reasons one would not think of building on the boundary. Especially if construction is planned on the second property – then perhaps a garden part directly borders the bedroom window (or similar).