Eberron: Ch.1 Political Theatre
All Dragonmarked houses are mercantile family/companies made of thousands of members. Each house controls major points of business in Eberron, but are still subject to ruling authority in whichever country they occupy. Houses may not control territories or create armies, and must remain politically neutral. Many members of a dragonmarked house do not possess a dragonmark themselves (fewer still possess marks of significant power), but almost all are related to someone who does. Members are not necessarily related to each other (but typically refer to one another as “cousin”) since a dragonmark can spontaneously manifest on any member of an appropriate species.