Our garden wall stands on the neighbor's property - is a notarized contract necessary?

An elderly gentleman has passed away, and the community of heirs is now suing the resident out. He was already informed in court that the written document has ZERO effect

That would be terrible... Just imagine if the deceased had sold you his house while alive and had kept the "live here forever contract" a secret from you...

Definitely in writing with a notary! There is a gentleman on this street who has lived in the house for 15 years and had it recorded in writing with the owner that he is allowed to live there forever.

Unlike property transfers, it would be new to me that a notary must be consulted for rental agreements. This sounds like a "lifelong" rental contract. No idea if something like that can be formulated in a legally secure way. But it is certainly difficult because it interferes with the economic independence of the heirs.

The OP could check whether a notarially certified usage for the wall (similar to a right of way/easement) might be possible. It would save a new survey and a donation would also not be an issue. But if it is to be permanent (i.e., even after the death of party A and B) it must be entered in the land register -> off to the notary.

The whole thing sounds like a "lifelong" rental contract. No idea if something like that can be formulated with legal certainty.

Not as a rental contract. Then a right of residence must be formulated ==> which inevitably goes through the notary again.

Not as a rental agreement. Then a right of residence must be formulated ==> this then necessarily has to go through the notary again.

Correct - that is the usual way with house or property handovers. But I am not familiar with that when dealing with a third party who actually lives in a tenancy. Also, with a real right of residence, the maintenance costs are to be borne by the entitled party (although this can probably be changed in the contract).

But towards a third party who actually lives in a disproportionate manner, I don’t know that.

That is quite normal. One can even grant the right of residence and at the same time have a rental agreement.

Also, with the right of residence as a real right, the maintenance costs have to be borne by the entitled party (although this can probably be changed in the contract).

Is it really different with rental agreements?