You don't include prepositional phrases in the number when matching verb to noun.
Correct: Ashley Randele and her parents, Tom and Kathy, were watching an episode of “NCIS.”
Correct: Ashley Randele, along with her parents Tom and Kathy, was watching an episode of “NCIS.”
Incorrect: Ashley Randele, along with her parents Tom and Kathy, were watching an episode of “NCIS.”
-PJ
Thanks PJT.