If Ygritte is used to steal (charagenda) Quentyn Martell (via Old Nan giving him the Night's Watch trait!) and then Valar is played, to whose House card does Quentyn go? We suspect it is the player who owns the Martell deck, as per the following note:
A Moribund card (and its attachments) is considered to have been killed, discarded, returned to its owner's hand or deck, or moved to its owner's shadows area, but only for the purposes of triggering responses and passive abilities. This includes responses and passive abilities triggered by a card being placed in the appropriate out-of-play area. A Moribund card is, for all other purposes, still considered in play.
However, we're not 100% sure...