Is boycotting a brother who causes problems at home and does not change despite quarreling justified, and is it excused in Islamic law?

If the estrangement from a brother is due to religious matters and his committing of reprehensible acts, then there is no harm in boycotting him. However, if it is due to worldly matters, then it is impermissible to forsake him for more than three [days]. It is better to be patient with him and continue advising him in the best manner, and to supplicate for his guidance.