They use the term "loyal fealty" as a statement of honour to differentiate them for the many traitorous vassals in the Seven Kingdoms. They serve as spies in the Crownlands feeding information to the mainline House Seywyth. As a cadet branch of House Seywyth they share in its wealth and repuation.
- Mortin Seywyth, younger brother and bannerman of Lord Dunstan Seywyth.
- His wife, Lady Olenna Seywyth. Eldest daughter of a prominent member of the Iron Bank of Bravos and Mortin's closest advisor. Known for both her immense beauty and her ability with political subterfuge.
- Their eldest son, Bryen Seywyth. Aspiring knight and a highly talented swordsman. Survived the Battle of the Blackwater undetected by the forces of House Lannister to return home to his family seat. He is Mortin's heir and possesses the keen military mind of his father and his mother's skill with political subterfuge.
- Their son, Corren Seywyth.
- Their daughter, Melianna Seywyth.
- Their youngest daughter, Celesse Seywyth.
- Their younger son, Tobas Seywyth.
- Ser Roderick Tavner, Master-at-Arms of House Seywyth of Romsey.
- Septa Elena, Septa of House Seywyth of Romsey. The personal tutor of Meliana and Celesse.
- Septon Orland, House Septon of House Seywyth of Romsey. Serves as the tutor of Corren and Tobas. Oversees the Romsey Sept.
- Kevan Loynton, Whisperer of House Seywyth of Romsey.
- Milene, captive wildling and kitchen servant.
- Irvin, Flea Bottom orphan and kitchen servant.
House Seywyth of Romsey is subject to the authority of House Seywyth. As a cadet branch it is of lower social status than the mainline house but shares in the reputation and military might of its overlord. It is protected by House Seywyth's personal army uses the same sigil as the mainline house. It has formed a number of alliances with other noble houses and prominent King's Landing personalities.
It also employs spies within King's Landing to eavesdrop on the goings on inside the Red Keep and in the circles of power. The house employs Laina, a prostitute in Flea Bottom, to spy on wealthy patrons who visit her brothel in exchange for protection and payment. It also employs a young courtier named Carrel in the Red Keep who provides it with information in exchange for favours. The house also uses a network of Whisperers and beggars scattered throughout the capital to provide it with a constant stream of information.