In the same predicate grammar, the singular is used for family members and the plural is used for family groups. Why?

In the same predicate grammar, the singular is used for family members and the plural is used for family groups. Why?

The form is singular, but the meaning can be singular or plural
Such collective nouns include family, team, class, audience, etc,
The features of its usage are: if it is regarded as a whole, it means singular; if it considers its individual members, it means plural
His family is large
His family are all waiting for him