The form of (1) is singular, but the meaning can be singular or plural. This kind of collective noun includes family, team, class, audience and so on. If regarded as a whole, it means singular meaning; If its single member is considered, it means plural meaning. For example:
His family is very big. His family is a big family.
His family are waiting for him. His family is waiting for him.
(2) The form is singular, but the meaning is always plural. This kind of collective noun includes cattle (cattle and livestock), people (people) and police (policemen). There is only a singular form, but it has a plural meaning. When it is used as the subject, the predicate is plural. Not used with (n), but can be used with. For example:
People will laugh at you. People will laugh at you.
The police are looking for him. The police are looking for him.
Many cows were killed for it. Many livestock were slaughtered as a result.
(3) The form is plural and the meaning is plural. This kind of collective noun includes goods, clothes, etc. These words only have plural forms (of course, they also have plural meanings, and the predicate is also plural when they are used as subjects), but they are usually not used with numerals. For example:
Clothes dry slowly in rainy season. Clothes don't dry easily in rainy season.
Such clothes are very expensive. Clothes like that are very expensive.
(4) Singularity in form and singularity in meaning. This kind of collective noun includes baggage/luggage, clothing, furniture, machinery, poetry, scenery, jewelry and equipment. These words are uncountable nouns with singular forms, no indefinite articles (not numerals, of course) and no plural forms. For example:
Our clothes protect us from the cold. Our clothes can keep out the cold.
Have you checked all your luggage? Have you checked all your luggage?
The thief stole all her jewels.
(4) Some collective noun means both singular and plural meanings.
When these collective noun are taken as a whole, they are singular, and when the predicate verb is the subject, it is also singular. For example:
This family is not big. (of the whole family)
The government has taken effective measures to solve the problem of laid-off workers.
When emphasizing the members of this group, it means plural, and the predicate verb uses plural as the subject. For example:
This family is all music lovers. (of a family)
The government will hold a meeting before making any major decisions.
Please note that these nouns also have plural forms when referring to a whole, but they refer to multiple such groups. For example:
Many families have this brand of washing machines.