Scott needs to talk to jean just after the pitfall game in murderworld
Magneto needs to be in your group at the very start of Mephistos realm
Sabretooth needs to be in your group when you battle gladiator
Dr. Doom nees to be in your group for the final fight with Doom.
These must be done in game.
Surfer is unlocked after you beat all of the comic disk missions, unless you put the code in.