Is it feasible to build a two-family house with parents / parents-in-law?

Just for understanding: Do the parents contribute 300k and expect free housing in return, or do they pay rent later or additionally pay for their living space?

If you have a slope where a basement practically suggests itself, then it makes sense to live there. If you want 150+85 sqm of living space "upstairs," that will result in correspondingly high usable space including the basement. That needs to be paid for.
Truly barrier-free living space is expensive and will require “the pièce de résistance” of the property to be realized.
Also think about the time after the parents, then you will have to bring in strangers and rent out the best part. In the middle of nowhere, sorry, you also have to find solvent tenants for that.


I lived on a split-level and can tell you, even as a young person who is not dependent on barrier-free access, I never want that again.

I would also not necessarily build split-level with small children. It is better to have as few stairs as possible.

Then an elevator or stairlift must probably be factored in, because:

True, completely overlooked that. But a stairlift would be cheaper than an additional floor as a storage room. Can you elaborate on that?

I wouldn’t necessarily build a split-level with small children either. The fewer stairs, the better.

If you have to, they learn impressively fast ;-) We didn’t have a single gate.

True, totally missed that. But a stairlift would be cheaper than an extra floor as a storage room.
Can you elaborate on that?

It’s just annoying. You can’t do anything without stairs in between, even though they are shorter than a normal flight of stairs. We already had three toilets in the house, yet you have to take a stair to get from the sofa to the toilet, for example. You carry everything over stairs, vacuuming is a pain. How many Roombas would you need …
And in the lowest floor you have friction losses – it’s either half a floor or an additional crawl space. You don’t really want that either.

The layout of the house at my parents-in-law's is similar to what is partly described here.
Slope property, ground floor + basement partly through the slope are grandparents' apartment, technical room, utility room, and basement room (which is effectively just a pure storage room).
Above is the "family apartment" on one level. We would want to do it something like that as well.

But of course, we want to sit down with a specialist at the appropriate time to use the possibilities effectively.

As rural as it sounds price-wise, it actually isn’t. The next town is 10-15 minutes away, and so is the highway. There is hardly any public transport except for students, but unfortunately, that is normal in Bavaria.

And yes, the plan is that my parents do not pay rent. However, if the entire project could not be financed like that, they would surely be willing to negotiate. They are very realistic about that.

and yes, the plan is that my parents don’t pay rent. However, if the whole project cannot be financed that way, they will surely be willing to negotiate. They are quite realistic about that.

Free rental to relatives is possible, but you lose the tax benefits that you would otherwise have as a landlord. That also has value.

But well, 300k is at least not completely unrealistic. We've had projects here in the range of 100k where the low-earning offspring were supposed to build an additional 70 sqm as compensation for the "gift." Of course, that is not a reasonable equivalent.