Purchase of land with an old barn that is also used by the neighbor

Good day. My name is Kai and I come from the Freiburg area. We would like to buy/survey and divide a 620m2 plot together with my wife's sister. There is an old burned-down semi-detached house on the plot, the neighbor next door has the other semi-detached house. We would also build a house there again. Everything is also clarified with the authorities. Now the actual question. Behind the house, there is a two-story barn on our property and on the neighbor's property (basically a barn semi-detached house). We have to completely tear down the barn on our side because we cannot use it for the building project. The barn is very old, and I think that if we partially tear it down, the neighbor will have the roof fall on his head in the barn. What do we have to legally consider? Can we just tear it down and does he have to take care of the stability on his side himself? Thank you very much in advance. Regards Kai

We also have semi-detached sheds/stables in our settlement. Many have already been demolished on one side.