Firstly, each card belongs to one ,or sometimes more, of the six great houses, unless it is neturtal. Can decks only be built using cards of the house you are playing and neutral cards? Or is it only cards with the text "House X only" that are restricted this way?
Also, when playing, can only one player play each house at a time, or is a game, for example, with 3 house Lannisters and 1 Baratheon possible? The drawback to that being, as I imagine, only that 3 players would share a number of unique cards and therefore limit one anothers options?