Artemis has a fear of trust (which could also tie in with her fear of people finding out who she is, but that’s an acute fear).
Lena has a fear of loss, which is only constantly reinforced her entire life.
Anya has a fear of the unknown, whether that’s large-scale or small-scale.
Warren has a fear of attachment and commitment, if you couldn’t already guess that.
Kai has a fear of people, not so much in the social way - just in general.