If you want to query patents by the size of the patent family, use the ANA_SFAM_CT field code.

Family size is an important value indicator in patent data.  Large families represent a large financial investment in patenting.  We use the DOCDB "simple family" definition when we develop patent families.  This means that all members share the same priority date.  The simple family contains foreign counterparts, continuations, and divisionals.  The simple family will contain CIP's only if they have the same priority date as the rest of the family.