Two-family house with 2 owners

I do not yet know if and when will follow my invitation to contribute here. However, the interim time does not need to be "used" to throw a small handful of framework facts with various derived fallacies into a cocktail shaker. So let's stick to the facts:

So, two couples (with still uncertain parallel family planning) and a plot of land that, even after a division, would not be allowed to be developed with a semi-detached house. That is a fact and forces a purely conceptual division (recommended as a condominium ownership) as a two-party house. In combination with separate financing, the legal form of the condominium follows as another factual necessity. The ownership shares do not need their own floor area; besides (not necessarily symmetrical!) semi-detached house form, they would also be possible as a classic two-family flat house (e.g., with a utility room in the attic). At this point, I’ll throw in, at least hypothetically, to once subject the friendship to a bunk bed test: who would let the other have precedence in a coin toss, who "sleeps on top"?

That both residential units would be sufficiently served by, let's say, a "shared combined heat and power unit" is economically also a fact and quite reasonable, which is why it will remain so. Behind that, meters can be installed for both parties as in a classic multi-family house. Reserving a blind second technical room in reserve for splitting the community seems excessive to me. How the joint technical center is operated can, in principle, be decided by the owners' assembly. Solely to avoid a stalemate, I recommend dividing the votes according to the special use areas. Practically, this could be most easily done so that (whether in a semi-detached or classic two-family house form) the utility room (if it mainly takes place in the attic, then the house entry room) is arranged so that effectively the unit closer to it becomes smaller as a result. For example, utility room attic 10 sqm, house entry room ground floor 3 sqm, apartment A 97 sqm and apartment B 100 sqm, garden for shared use would result in co-owner B having 100/197 voting rights shares to decide in a dispute. Is the friendship still stable at this point in the text?

As long as the separateness is maintained (each unit requires cooking facilities and a toilet), one may completely fill the rest of a house with house connection rooms. Multiple meters can also be connected for hot water storage tanks. And I have never heard of a single case where, in one of the countless six-family houses divided into condominiums, a four-sixths co-owner told the others to acquire their own boilers because he was terminating their connection to the shared heat supply. The residual risk of a lunar eclipse on the Day of Never is hardly eliminable. Therefore, on top of belt and suspenders, taking out insurance at Hypochondria—one can also overdo everything.

Conceptual or as a condominium, no development plan limits the number of entrance doors. Presumably, two residential units per plot are permitted here, and it is intended to avoid that 4 residential units (= 6 or 8 parking spaces) arise on the property.

So: talk to each other, do the bunk bed test. Depending on the result, my tendency here would either be to build a classic two-family house or choose the "conceptual semi-detached house." Either way, follow my warning about the stalemate (there is little way around it with the condominium due to financing) and "build" a slight asymmetry of the voting ratios (where, in my model, the same party that "gives up" the area for the shared technical room would also have to endure being outvoted) or provide a redundancy reserve of a potential second utility room. You will have to die one way or another; washing without getting wet is impossible.

I have done pretty much exactly what you intend to do or am currently in the final construction phase of the project.

Currently, the house connection room/utility room is arranged so that it requires 6 sqm of floor space from each party on the ground floor. Basically, you could simply run the partition wall of both housing units through the utility room, then each would have their own. Only the house connections would then, of course, be either on the left or right side.

Currently, the house connection room/utility room is arranged in such a way that it requires 6 sqm of floor space from each party on the ground floor.

I had the same thought, apart from the additional costs (even if it then means two smaller heat pumps instead of one large one), of course a sufficiently large utility room would have to be planned in each half, which of course again reduces the living space.

Currently, the house connection room/utility room is arranged so that it requires 6 sqm of floor space for each party on the ground floor. In principle, you could just pull the partition wall of both residential units through the utility room, then each would have their own.
Only the house connections would, of course, then lie either on the left or right side.

(Where) have we already discussed this here?