Is construction possible on this property?

Why do you believe the opposite?

For example, someone wrote: it will be very difficult to impossible to accommodate an extension of the desired size on plot number 23. With the corner plot number 25, the chances of achieving a sensible arrangement would be much higher.

I don't believe anything, but have only answered your question based on the details mentioned: 210 sqm living space in 2 residential units is basically possible here, on plot 23 and others. Plot 25 is even 28 sqm smaller. So if it is supposed to be more suitable or cheaper nevertheless, it must be due to conditions that have not yet been mentioned to me. If it is already about very specific house designs that are to be glued together as unequal twins and we do not know which ones: then we cannot take that into account yet either. But then a redesign might be possible, because as said: basically, no suitability exclusion can be seen.

Now we would like to build something like what is shown in the pictures.

Thank you for your answer. Now we would like to build something like what can be seen in the pictures.

I would prefer the left example. Am I correct in assuming that the lodgers are the (parents-in-law) of the building couple, and that no real division of the property between the floor areas of both residential units is planned anyway? - then I would suggest giving the seniors more ground floor and the "youth" more upper floor, have a look at this thread:

Am I imagining this correctly (see attachment)?