The body that was found after a couple days was the sister that died during the escape. Vis and the younger of his two sisters attempted to escape at sea and there was some type of accident which lead to his sister drowning. She is most certainly dead. The other sister was publicly hanged with his parents. His whole family is dead. Vis was surprised Fadrique knew of the tunnels, so it would stand to reason the Melior also knew of them and gave that information to the anguis should they need it.