I wonder if there is any difference between the following two sentences?
They are a member of a committee.
They are members of a committee.
In the first example, it is the singular use of they, whereas the second example, it is a plural usage. Singular they is often used to be gender-neutral, instead of using he or she.
If you were referring to a single person, then the first form would be correct. However, if you were referring to more than one person, the second form would be correct.