Building a house on (partially) someone else's land

You need a declaration of division to divide into residential property.

Exactly: one gets the residential property, the other two each get, for example, a garden share. With several condominiums, one also gets more, one less (depending on the square meter size of the apartment), while another might get an additional parking space and the ground floor apartment perhaps assigned the garden.

The bank also wants to register a property

exactly: one gets the residential property, the other two each get, for example, a garden share.

This does not work like that. You need at least two apartments/houses in order to be able to divide. These apartments/houses then actually belong to one person. The land itself belongs to the entire community!!! and the respective owner of the apartments/houses only gets the right of use (and obligations). For such a construct to work for the OP, three apartments/houses are needed for a fair division. For an unequal division at least two. The OP has to comment on what, why, and how he plans.

Thank you very much for your numerous helpful answers, they really help me a lot. I did not know to what extent it is relevant how many residential units are involved. Here are some concrete data for my case:

Division of the property:
Son1: 1 part
Son2: 1 part
Parents as a married couple: 1 part

Planned construction of a semi-detached house:
Half1: Son1 (as owner-occupied home)
Half2: Son2 (for renting out)

Do special applications have to be submitted for such a constellation? Who can best help me with all these questions? Tax advisor? Contractor?

The arrangement with the division of the property was thought up by my father so that it essentially stays in the family in case there are problems later with a future wife or similar (divorce, etc.). So it is purely a precautionary measure, which of course does not exclude/guarantee against internal family disputes.

To my knowledge, a building permit is granted subject to the rights of third parties. So the building authority is probably less interested, at least at first, in exactly who owns the property.

I really love such great constellations to exclude women. Not. I hope your partner also does not financially participate in the project and that you are already thinking about inheritance and so on. Or should the ladies move out when the involved brothers die before them?

Plot distribution:
Son1: 1 part
Son2: 1 part
Parents as spouses: 1 part

planned semi-detached house development:
Half1: Son1 (as own home)
Half2: Son2 (for renting out)

MESS!

Go to a notary and tax advisor. In the intended form, this does not work. The two houses will belong 1/3 to Son 1, 1/3 to Son 2 and 1/3 to the parents, since they stand on the common plot. Dividing the plot physically does not help either. It’s total nonsense on a smaller scale. Building in a WEG also does not work structurally. Financing is also catastrophic. Tax allocation is the same (because Son 1 and the spouses also become landlords).

Sorry, but your father has no idea about the subject. A specialist is needed who can turn your father’s intention into a manageable structure.

What makes sense is a physical division and a clean transfer to you sons. Then you will also have to agree with your (future) wives on who contributes financially how. Paying as a wife for a house that belongs to the family is not nice. Maria16 has already said something about that.