I find it sensible to be realistic, but that it is unthinkable for a family to "stay together" seems a bit pessimistic to me. If nothing can develop, nothing develops either.
In my opinion, one should not expect that everyone stays in one place, but making sure of it - making it possible - does not seem wrong to me. In my environment, there are several patchwork "families" or "groups of friends" for whom favorable architecture is helpful.
From my experience, the most important thing is not having to share rooms like the kitchen and bathroom, because the potential for frustration is high there, but living close to people you like is something I find desirable. If my neighbors are not randomly mixed people but my friends - or otherwise close - that is pleasant for me.
For us (my wife has a talent for this and I like to be involved :)) such connections have developed. Not that there wouldn’t be any trouble then, but among friends you cope with it much more easily.
At the moment, for example, we are expanding the space in our house (with a bathroom and possible kitchen), although we are already managing well – simply because the attic exists and it would be a waste not to use it. Whether someone will move in – and who that could be – is still open :D
I just mean :cool: