What Qur'anic verses and prophetic hadiths can be used to deter someone who is trying to seduce his brother's wife, to prevent him from falling into indecency?

You must advise your brother and clarify for him the gravity of this sin. The Sacred Law prohibits entering upon women out of fear of falling into immorality. Committing a sin with a neighbor is one of the greatest sins and major transgressions, as indicated by the words of the Messenger of Allah, peace and blessings be upon him: "The in-law is death," and his saying when asked about the greatest sins: "That you commit adultery with the wife of your neighbor." You must conceal his sin if he is not openly defiant with it.