How many residential units are possible?

If you want to build 2 residential units on the property, 10m can already be quite tight.

You only need to add 100 m2 to the large property. Then everything is settled. If possible, build without an easement.

You just need to add 100 m2 to the large GS. Then everything is settled. If possible, build without an easement.

If you want to build 2 residential units on the property, 10m can already be quite tight.

You only need to add 100 m2 to the large property. Then everything is settled. If possible, build without an easement.

I think the matter with the two residential units is settled anyway. If anything, something small will be built there when the government boosts housing construction a bit more.

The idea of adding 100m2 was also mine, but then I would have to get a surveyor involved again. What would be the easiest and cheapest way?

If anything, something small for copying will be put there, [...] but then I will have to bring a surveyor on board again.

You can also copy the surveyor.

The idea of acquiring the 100m2 was also my thought, but then I would have to involve a surveyor again. What would be the simplest and cheapest way?

To build 3 residential units, this is the most reasonable way. The surveying costs are worth it to avoid having a notional division.