Can you see why the sentence below has a subject-verb agreement issue?
Everyone in the family, including the children, are going to the beach.
If it looks and sounds correct, then you probably think that children is the subject of the sentence, and because children is plural, and the verb are is plural, it must be correct, right? Yes, children is plural and it’s the noun closest to the verb, but children is NOT the subject of the sentence. Everyone is the singular subject of the sentence, and are is the plural verb, so they are not in agreement. The verb should agree with the subject, no matter what modifying words or phrases come in between. Here is another example:
One of the team members are leaving.
Again, the subject is the singular one, and although members is plural, it is the object of the prepositional phrase of the team members, and does not determine whether the sentence takes a singular or plural verb. The sentence should read:
One of the team members is leaving.
The key is to correctly identify the subject and remember to disregard any modifiers that may be located in between the subject(s) and verb(s) in the sentence.