Below details provide help with creating a new Family based on a Family or copy a family to the same Catalog,
1. Open the existing family in New / Modify Family by either right-click on the Family in Catalog Manager or by opening the Family from Manage >> Create Family >> Open >>Select the Family for example 21 as seen in the below image.
2. Now in the open Family make the required changes and select Save As, Specify the name for the Family an select the Catalog to be saved in, and select Save.