From what I know theres a total of 18 games in the Atelier series. Not counting the remakes and ports.
Atelier Marie: The Alchemist of Salburg
Atelier Elie: The Alchemist of Salburg 2
Atelier Lilie: The Alchemist of Salburg 3
Atelier Judie: The Alchemist of Gramnad
Atelier Viorate: The Alchemist of Gramnad 2
Atelier Iris: Eternal mana
Atelier Iris 2: The Azoth of Destiny
Atelier Iris 3: Grand Phantasm
Mana Khemia: Alchemists of Al-Revis
Mana Khemia 2: Fall of Alchemy
Atelier Rorona: Alchemist of Arland
Atelier Totori: Alchemist of Arland 2
Atelier Meruru: Alchemist of Arland 3
Hermina and Culus: Atelier Lilie Another Story
Atelier Marie, Elie & Anis: Message on the Gentle Breeze
Atelier Lise: The Alchemist of Order
Atelier Annie: Alchemists of Sera Island
Atelier Lina: The Alchemist of Strahl