While Yosef recognized his brothers, they did not recognize him.
I heard a Rosh Yeshiva suggest that Binyamin, who wasn't so absorbed in the soap opera, was able to recognize Yosef, but played along the whole time.
The verses really don't seem to address it. Benyamin is a total sock monkey through the whole story; he doesn't say or do anything, he's just acted upon.
(Yes there's the midrash how Benyamin tells Tzofnas Paaneach that he has ten sons, all named after his long-lost brother; but of course you could read that one either way too ...)
Has anyone ever heard this before? Any commentaries suggest it? Any arguments for or against the possibility?