The reason groups of families cannot live together, even when economic necessity requires, is that our sociocultural reality is splintered severely. Each individual is an island who thinks they are 100% in control of the norms and standards of their life, outside of the legal constraints of the state (which, ironically, are many).
Groups of 3 to 5 families with, say, 5 or 6 attached single adults could inhabit a large mansion with small condo units for the families and apartments for the single adults and with most meals eaten together in a great room, and many shared facilities. Paying less than is needed now for housing, they could literally enjoy the fringe benefits normally accorded the very wealthy. If they did a lot of rhe building work together, and endured a time living in a single cramped house for a year, they would save even more money.
This is logical. But the inviduation of culture prevents this. They would have wildly different diets, different beliefs and convictions about rasing kids, different beliefs about what is acceptable in entertainment, and on and on.
Close physical proximity and close sharing of resources requires close proximity of beliefs and convictions about how to live. To come together within the context of a national identity defined by a covenant instead of blood or territory means nobody gets 100% what they want, but nobody has serious moral objections, and everyone is willing to make modifications and adjustments for the sake of harmony that don't seriously threaten their individuality.
My breakthrough idea is the power of shared nationhood based on an explicit and freewill covenant association. I literally have such a nation in mind, but this idea can apply to any nation as a people.
I'll take the Igbo. One of my favorite nations. They are more or less Christian. They have their own traditions and myths. They have a unique way of life. If I wanted to reinvigorate the Igbo I would gather the elders and most respected people and say, "draw up a national covenant between your nation and God, make it explicit, and make adherence to that covenant the basis of your nationality." Thereafter groups of Igbo families and their attached single adults would be able to cone together on the basis of the national covenant and act as one household in terms of mutual care.
Making national covenants explicit and making them the basis of your nationhood can bind large numbers of families together, and they become the basis of smaller groups of people being able to live together as much larger and mutually supportive households which do not suppress or interfere with individuality.
If I wanted to reinvigorate the American Christian nation, an American nationhood shared among American Christians, I would take a similar approach and form a Society based on that identity and covenant. I am not suggesting that only Christians are Americans, that horse has left the barn. This is, in part, why I prefer a whole new and intentional nationhood.
Of course we Christians are part of an eternal and universal nation, and every Christian nation on earth represents a unique facet of that nation. Spiritual Israel and the Kingdom of God are not monochromatic! Unique and diverse temporal nations based on a shared covenant bond are God's ordained prime movers of human civilization down to the level of the family.