Amiri will join you after the prologue.
Linzi, Valerie, Harrim and Jaethal will be decided by your choices at the end of the prologue. You'll need to choose good or evil and chaos or law. Good gets Linzi, Evil gets Jaethal, chaos gets Harrim, and law gets Valerie. Then, you can pick up one of the two you missed at the ancient tomb and another in the kobold camp at old Sycamore.
Tristian is at the Temple of the Elk.
Octavia and Regongar are at the Technic League Encampment.
Jubilost is at the Ford Across Skunk River during Troll trouble. He might refuse to join at first. Talk to him again after defeating the trolls to recruit him. Can definitely be missed.
Ekundayo is at the ruined watchtower during Troll Trouble. Follow the dog.
Nok-Nok is at the goblin village during the season of Bloom.