I'm guessing "La pareja" is treated as a singular. "La pareja comentaron sobre " has only 2 google hits and "La pareja comentó sobre " has 448 hits. Using a more common verb "La pareja bebe" 14,700 results and "La pareja beben" 7 results.
The bird commented on them. No wait, that's obviously gibberish. (Although I can think of a verb which would make the sentence completely sensible.) Hm. Párajo, Pareja. Is spanish trying to tell us something? Let's try, the couple gossiped about them. Means almost the same thing. Nope. Apparently not right either.