They had recently been knighted when Lancelot stopped at Astolat on his way to the Winchester tournament. The main importance of the older brother, Tirre, seems to be that he had been wounded the same day he was made knight and was still lying abed with his wounds, so that his shield was available for Lancelot to borrow. Lavaine, the younger son, went with Lancelot to the tournament, made a good showing, and helped the gravely wounded Lancelot away to the hermit Baudwin.
Returning to Winchester - apparently sent by Lancelot to seek Bors or some other kinsman - Lavaine first encountered his sister Elaine and later located Bors, bringing them both to the wounded Lancelot. Lavaine remained at court after Elaine's death,
and ever in all places Sir Lavaine gat great worship so that he was renowned among many knights of the Table Round.
In Arthur's Christmas tournament, Lavaine encountered Arthur himself in the lists and they smote each other down. Made a companion of the Round Table at the same time as Sir Urre of Hungary, Lavaine married Urre's sister Felelolie.
Remaining in Lancelot's faction during the break with Arthur, Lavaine accompanied Lancelot into exile and was made Earl of Arminak (Armagnac).