How small is the town, district, or whatever it is that everyone directly calls the mayor?? He behaves like the Sun King. From my perspective as a big city resident, this seems completely absurd. Reads like an episode of Paw Patrol.
You urgently need to bring order and structure to the situation. There are official plans and official changes made by authorities when something happens. That is what matters! Customary law counts less, and certainly not what a real estate agent promised you. So, get the plans and create a chronologically clear list.
Now you say the property is worth 1.6 million euros. With such high assets, an appropriate lawyer would be more than suitable for you and worth every cent.
PS: Upon another reading, it turns out you always talk about one property, but in fact, there are four? Maybe even more. : If you’re still following here, please post at least one current, anonymized cadastral map.