。
All of my companions were asleep.
Literal
Companions [subject-が] all were-sleeping.
A simple narrative past-progressive sentence. 仲間 ('companions / comrades') implies a close group — friends, teammates, or fellow travelers. すべて ('all') modifies the subject. 寝ていた is the past progressive of 寝る, marking the ongoing state of being asleep at a narrative moment. Short and evocative — the kind of sentence that sets up a scene where the narrator is alone while everyone else sleeps.