The sovereign domains, spoken plural — the Sanctuary's many houses under one sky, each with its own laws.
The plural of realm, from Old French reaume, from Vulgar Latin regalimen, from Latin regalis (royal); spoken plural, the word names many separately governed territories rather than one large one.
The sovereign domains, spoken plural — the house's many separately governed houses under one sky. The plural is the point: each realm keeps its own root of authority rather than sharing a single one.