إِذْ هُمْ عَلَيْهَا قُعُودٌۭ
Sentence structure
إِذْ introduces the time clause. هُمْ is its topic, قُعُودٌ the nominative predicate, and عَلَيْهَا is linked to that predicate.
Ayah summary
They sat around that fire.
إِذْ — When
Grammar: A time adverb introducing the following nominal clause; its wider attachment is not made a scored fact.
هُمْ — they
Grammar: A third-person masculine-plural detached pronoun functioning as the topic.
عَلَيْهَا — by it
Grammar: عَلَىٰ is a preposition and attached هَا its genitive pronoun; the phrase is linked to قُعُودٌ.
قُعُودٌۭ — (were) sitting
Grammar: An indefinite nominative verbal noun functioning as the predicate of هُمْ.