Sounds like you're talking about collective nouns. Here's a handy guide I pulled from the Canadian Government's Translation Bureau:
Singular and plural verbs with collective nouns
-A plural collective noun takes a plural verb: Families enjoy this restaurant.
-A singular collective noun usually takes a singular verb: Our family enjoys this restaurant.
-But there are some cases where a singular collective noun actually expresses a plural idea and needs a plural verb. The guidelines below will help you decide whether a singular collective noun takes a singular or plural verb.
When to use a singular verb
-When all the members of a collective noun are performing an action as a unit (and that’s usually the case), use a singular verb.
-The chamber orchestra often plays at the Art Centre.
The cast is celebrating the success of the play with a party after the performance.
-A wolf pack hunts as a group.
-The fleet was anchored in the channel.
When to use a plural verb
When the members of a collective noun are performing an action as individuals, use a plural verb. In this case, all or some members of the group are doing something independently of the other members; the group is not acting together as a unit.
-The orchestra are tuning their instruments.
-The cast have been practising their lines.
-The flock were running off in every direction.
-The staff disagree on the proposal.
In many cases, it may sound more natural to make the subject plural in form by adding a word like members:
-The members of the orchestra are tuning their instruments.
-The cast members have been practising their lines.
-The staff members disagree on the proposal.