Nuclear family refers to the centralization of the family, in the home, with parts that roam about but always come back. The two gendered parents for a firm bond that keeps the "molecule" stable. Children, pets, etc are like the atoms that spin around the firm center. This is if my memory serves me well, it has been a number of years.
1.0 Red-Tailed Boa
1.1 Amel Corn Snakes
1.0 Jungle x Coastal Carpet Python