At that time, we built under almost the same conditions. My parents had sold their terraced house and given us a similar amount in DM. In return, we built a nice 90sqm apartment for them on the upper floor. They didn’t pay rent, but in an emergency they would have done so, though that never happened. We young people were the owners of the whole thing and they had the right to live there; the whole arrangement was registered with the notary. It became difficult many years later during the divorce... then there are completely different problems besides the paperwork. In the end, my wife (unfortunately) moved out with the children and I moved back in alone. There was no quarrel, nevertheless it was not how it was intended, which I could understand. In hindsight, I had the units divided into 3 apartments: upper floor, ground floor, basement. I still find it a very sensible and nice way of living, even though it didn’t quite work out for us until the "end". It mainly depends on whether someone is intrusive or likes to be overly close; we had cleared that up on both sides beforehand, and basically it was never a problem. But one should honestly examine that within oneself, and this in both directions. Everyone knocked before entering the other’s area, that’s also what we taught the children. I am always somewhat cautious about the topic "barrier-free". Similar to burglary protection, it is in many respects a standard. In our case, we gave the notarial commitment of "care and maintenance", which is, of course, vague, but beyond that our word applied, which was sufficient for both sides. Nevertheless, it should be noted that changes can come, and what/ how it will be then with the parents-in-law; the notary will point out the circumstances to you, maybe separate ownership is better after all—? For me, the promised care does not mean the often described or feared "wiping of the bottom," but the assumption of responsibility. Our father was “cared for” for many years, partly by the nursing service, but mostly by my mother. Things like personal hygiene and others can be done by the nursing service, but the daily closeness, caring for the many little things and taking time are super possible in such a constellation, and loneliness in my opinion is the biggest problem of an old person. Costs for garbage, telephone, magazines and all the other things are shared, in my opinion a very big advantage for both sides besides the togetherness. We then retrofitted various things like, for example, a grab handle here and there, a bathtub lift, and much more, all things that can be easily retrofitted in any apartment. I certainly do not want to say anything against "barrier-free," but just to point out that upcoming problems can only be partially caught by it. In most of the cases I know, the problems lie in the mental area. When the older person can no longer walk well, he will rarely go out of the house and if so, accompanied. Then we went up and down the stairs with help, that was 5 minutes twice a week. If you as a family live in the same house, that already fulfills more than barrier-free could achieve; nevertheless, one can make provisions for possible things without becoming too expensive. Separate entrances and privacy from BOTH sides I would try to implement but also not desperately. An intrusive person manages to annoy you everywhere, a person with respect does not annoy you even if he only sits separated from you by a plant. Therefore, I would not look at it only technically (but also), the decisive factor is the HOW, which can already be recognized beforehand by closely observing (also yourself). We had a shared laundry room but that was separable later as well. The good thing about it is that you can sell/rent separate units later. You may not want to, but it is possible; for me, it was the "rescue" at the time, otherwise the house would have been lost.
