How sound are the actions of a brother who married secretly after his parents' refusal, and is that considered disobedience to parents? And is his parents disowning him and his siblings boycotting him considered correct, or is it a severance of kin ties? And what is the role of the siblings in attempting reconciliation?

The brother should not have disobeyed his parents regarding marriage to that girl unless he feared falling into sin. In that case, he is excused for concealing the marriage and is not considered disobedient as long as he does not abandon them. The parents should not abandon their son; rather, they should show compassion and offer advice. Similarly, the siblings should not boycott their brother; instead, they should strive to reconcile and unite the family, appease the parents, and advise their brother. Wisdom should be exercised in handling the matter, for reconciling disputes is one of the greatest acts of worship, and it is among the matters in which lying is permissible.