1) Ideelle division means 50 : 50, regardless of what is stated. It is annoying when the houses are unevenly sized and/or have unequal features. 2) Division into WEG is possible, but a completion certificate must be available before construction begins, i.e. the plans for both houses must be final. The declaration of division must be prepared by the notary. 3) Real division does cost the surveying, but it is clean. Everyone can sell/encumber their part as they wish. Like others, I would recommend 3). The question remains whether a pipe-head property with assumption of setback areas or a path / utility easement. It actually does not matter. Both must be registered in the land register. The advantage of each variant depends on how concretely the construction is planned, i.e. also whether, for example, the access path to the rear property is also to be used as an access path by the front property or something completely separate is planned here. Given the overall volume (2x new construction!) my tip is to proceed cleanly here and invest the 5K€ for the division.