Welcome bro though I'm sure someone would have posted it up if I didn't made it. To unlock Sasuke you have to beat Akatsuki Mode with Itachi (Not on Hard or anything, just play with Itachi), for Sai I'm not sure yet.
at first i got the game and thought, wow thats how much characters you get? then i went to akatsuki mode and i got so many more. i tried to get the akatsuki leaders character, but later found out he wasnot availabe. that would be some god dlc content on the psn