"Nuclear" should mean that newly married couples form a new household rather than integrating into the household of the extended family.
Why the nuclear rather than the extended family would be considered important for social stability is anyone's guess. We live in an incredibly atomized society that values personal freedom and autonomy over interdependence and social connection, but that doesn't mean "stability".
Why the nuclear rather than the extended family would be considered important for social stability is anyone's guess. We live in an incredibly atomized society that values personal freedom and autonomy over interdependence and social connection, but that doesn't mean "stability".