My brother is going to marry a Mutabarrijah (a woman who makes a public display of her charms or adornment). What is my duty towards him?
What is your advice for him after their engagement? What should I do if they use musical instruments to celebrate the wedding at home?
You should advise him to marry a religious woman, in obedience to the saying of the Prophet (peace be upon him):
"...So try to get one who is religious."
Do not attend a wedding party where musical instruments are used unless you are able to resist evil; otherwise, you should avoid the evil. (Part No. 17; Page No. 183) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.