What is the way to deal with a brother who displays hatred and malice through his actions, yet claims otherwise verbally, and spoils the relationship with the rest of the siblings who ask me to prove good faith?

We advise you to be good to your brothers, treat them kindly, and be generous to them to the best of your ability, while respecting them, revering their elders, and showing mercy to their young. Respond to their ill-treatment with kindness, for by doing so you will attain the companionship of Allah, and Allah will make them love you. Allah Almighty says: "And not equal are the good deed and the bad. Repel [evil] with that which is better, and thereupon the one whom between you and him is enmity [will become] as though he was a devoted friend."