They're all unlocked after completing the third film story (At World's End) but after that they have to be bought while walking around in the port hub area.
Characters required for this achievement :
*Mistress Ching -- Buy for 25,000 Studs. Found on The Brethren Court in At World’s End. Unlock Code: GDETDE
*Sri Sumbhajee Angria -- Buy for 25,000 Studs. Found on The Brethren Court in At World’s End.
*Gentleman Jocard -- Buy for 25,000 Studs. Found on The Brethren Court in At World’s End.
*Ammand the Corsair-- Buy for 25,000 Studs. Found on The Brethren Court in At World’s End. Unlock Code: EW8T6T
*Eduardo Villanueva -- Buy for 25,000 Studs. Found on The Brethren Court in At World’s End.
*Capitaine Chevalle -- Buy for 25,000 Studs. Found on The Brethren Court in At World’s End.
*Jack Sparrow (Cursed) -- Buy for 100,000 Studs. You WILL need. Unlock Code: VDJSPW
*Captain Barbosa -- You might need.
Credit for video GameGuideCentral;