The issue is that across the movement of time and generations a "nuclear family" unit of parents and their offspring has all the stability and longevity of a pencil balanced on it's tip .. the clock is ticking on Hapsberg lips and the oddities of pharoahs.

Long lasting societies have a larger formal weave based on outworking and out breeding, formally moieties in the indigenous peoples of North America, Australia, Indonesia and elsewhere.

A single family unit alone is insufficient and historically cycles members in and out over half a generation through marriage and fortune seeking.

I've seen your other comments and they have that kind of first order depth expected of a simple thought and looking things up quickly on a phone.

Here's a very shallow introduction to a family of systems with many variations that lasted some 70 thousand years keeping bloodlines clean: https://en.wikipedia.org/wiki/Moiety_(kinship)