2. What are the requirements I must meet in order to receive the above funding (aside from the energy supply already designed for 2 parties, i.e., two circuits, 2 lockable residential units)?
Residential units are rooms within a closed context intended for permanent residential purposes in residential buildings, which enable the running of a household (room, kitchen/kitchenette, and bathroom/WC).
1. If I plan the house as a two-family house from the beginning, can I then claim 2 x KfW funding?
Yes, but there are several things to consider in terms of planning, execution, and cost. Interior doors do not count as residential unit doors, etc. Either you need 2 apartment doors that open to the outside or a corridor that is not assigned to either of the "apartments."
2 circuits That means 2 complete electrical panels, with meters ... (and numerous circuits)
Since the funding authority can and may inspect the actual situation, the living situation to be created when there are 2 residential units is not really "livable."
So, the 5000 repayment subsidy is already lost just due to the additional costs. And the 10-15,000 EUR that you could save over e.g. 30 years might also definitely be lost for the 2 residential units solution.
Additionally, the buildable plots are restricted. In many newer development plans, the number of residential units is specified.