Narrow access to the building plot / crossing neighbor's property

Hello everyone,

we have purchased a property with a large plot of land. We want to rent it out and build in the garden ourselves. The buildability has already been clarified. Unfortunately, the property has a narrow access road (2.50m) to the garden.
We have been in contact with the manager of the neighboring property since November. He informed us that the owner agrees but wants this to be notarized so that he can also use our driveway in the event of a possible construction. We had the agreement drawn up, sent it to him, covered the costs, but unfortunately have not received any feedback. We have now contacted the owner himself again, but unfortunately no response there either. He unfortunately lives in the USA, otherwise we would have liked to meet him in person.

Our questions now:
We have oral consent; are we allowed to cross the property for construction?
Is there possibly a way to "force" the neighbor to agree to the crossing?
And: Are there other options? Maybe to lift the material completely over the existing property with a crane? We have space for a crane in the front garden.

We look forward to your answers!

Kind regards

What is the plan supposed to say, that is, what is your property, which one do you want to cross?

The keyword for you is "Hammerschlags- und Leiterrecht". And as is often the case in DE: It depends.

not only the distance from the house to the boundary is important, but also what is above,
eaves trough, gutter, downpipe, etc.
otherwise also the load-bearing capacity of the walls of the front house, in the case of a 40t construction road

thank you very much for your answer. Our property is number 135 and we want to use part of the driveway of 133. We have already deducted the roof overhang at 2.50 m. We have already commissioned a structural engineer to assess the existing building and its load-bearing capacity.