Returns the number of families in which a given Individual is
listed as a spouse or parent.
Note: the term 'spouse' is used a
little loosely here. Family records are used to record not
just marriages, but also long-standing relationships between couples
who never married (as well as for recording parent-child
relationships). Unmarried parents or an unmarried couple,
recorded in this way, count as 'spouses' for present purposes, even
though strictly they aren't spouses.