The Gawain character looks like a fusion of the Merlin and Escanor characters (the strength of Escanor and the magic of Merlin) . The Spanish Nanatsu no Taizai wiki claims she's the daughter of both of them, which I doubt because the English wikia says nothing. Gawain - Nanatsu no Taizai Spanish wikia
Also, this other article in a prestigious Spanish sports magazine, which uploaded an anime article for some reason, claims she's the daughter of Diane and King Who are the 4 knights of the Apocalypse - Mundo Deportivo
Is Gawain related to Escanor and Merlin? How about to Diane and King?