1. Where are the other prisoners?
they died when the bombs hit the plane?

2. When did Mohinder met Hiro before? He speaks to him as they had met before...

1. No clue. Probably rounded up or dead.

2. Mohinder never met Hiro before. Mohinder said "You lost your ability, how? ... From what I've heard it would have been quite useful today."

Did anyone notice that Hiro referred to Ando as "evil Ando?" He did say "evil" right?

i do not recall them meeting,but he obviously knows of hiros powers hence season 1 future hiro stopping time while peter and him were on the subway together