Sora recognized masked Vanitas, but was shocked by his face when the mask broke. He saw Vanitas unmasked in the last game, so it's impossible for Sora to react surprised.
Hayner, Pence and Olette were NEVER friends with Roxas. They met him once when Roxas say Hayner failing at Grandstanding during his Day Off. Pence met Roxas and Axel briefly when he was investigating the Wonders but never paid much mind.