Validate their feelings - Acknowledge how the siblings feel and lead them to an open discussion. Heart issues and hurt feelings that have not been acknowledged early on can cause depression, regrets and lack of motivation in your children when they turn adults. Let them express how their anger, fear or frustration and let them know that you understand why they feel that way. However, don't forget to correct such destructive feelings.
Enforce forgiveness - Stop your children from blaming and throwing verbal insults at each other. Encourage them to forgive each other and to start a new with their sibling relationship. Teach them ways on how to rebuild their trust on each other so that they can grow old together not holding grudges.