First, consider basic subject-verb-antecedent agreement. The best way to think about the subject of the sentence is by asking the question "who" or "what" is doing something. The answer is your subject. Next, ask what is being done. The answer is the verb. Last, see if there is a pronoun in the sentence that stands in for the subject. If so, this word is the antecedent. For example, look at the sentence "Sarah pays all of her bills online." The "who" (subject) is "Sarah," "pays" answers "what" (verb) she does and "her" (antecedent) is the pronoun that represents "Sarah."
Not all sentences contain a single subject like "Sarah." However, sentences that contain a word that represents more than one person or thing but operates as a single entity are called collective nouns and, for the most part, are considered singular. Some examples of collective nouns are "team," family," "jury," "committee," and "crowd." The antecedent, then, is also singular.
Take this sample sentence: "The crowd was on its feet the minute the band stepped on stage." Here the crowd is acting as a single entity, so the verb "was" and the antecedent "its" are both singular.
Sometimes, collective nouns represent people in the group acting as individuals. In this case, the verb and antecedent are plural: "The family cleared the table and then went to their rooms." "Family" is the collective noun subject, but each family member acts as an individual--each is returning to a room--so "family" is plural. Likewise, the antecedent "their" is also plural.
If you are using a collective noun that has a plural meaning, add a plural noun to clarify. An example from "A Writer's Resource: A Handbook for Writing and Research" offers a great example of adding a modifying phrase. Sentence 1: "The group were passing around a bottle of beer." In this sentence, the "group" is made of individuals acting independently, but the sentence sounds odd and isn't completely clear. Here's a way to modify for clarification: "The group of troublemakers were passing around a bottle of beer." Adding the plural noun "troublemakers" helps make clear the sentence's meaning.
To clarify the sentence about the family clearing the table, try adding "members," as in "The family members cleared the table and then went to their rooms."
Grammar checkers do not always catch pronoun-antecedent agreement or pronoun reference problems. It is best to not rely on them but to check your work by reading it aloud to yourself or having someone else proofread if you are not sure of a potential problem.