Sera
Affiliated Quest: A Friend of Red Jenny
After the meeting with Mother Hevara, listen for the sound of an arrow striking nearby. Interact with the arrow to begin A Friend of Red Jenny. After helping Sera dispatch some enemies, you have the opportunity to recruit her.
Vivienne
Affiliated Quest: The Imperial Enchanter
Look for a messenger in Val Royeaux extending an invitation to the Ghyslain Estate. Travel there on the world map to meet Vivienne. After a brief conversation you can invite her to the Inquisition.