How is it possible to financially support a Hindu brother who is about to get married and accompany him to his wedding ceremony, especially after his previous supportive stances in defending the questioner's religion and helping him settle his debt?

It is permissible to maintain ties with a disbelieving brother through money and gifts, especially if he has taken good stances, to reward him for that, based on the Almighty's saying: (Allah does not forbid you from those who do not fight you because of religion and do not expel you from your homes - from being righteous toward them and acting justly toward them. Indeed, Allah loves those who act justly).