Here are some grief support resources you might find helpful:
FOR THOSE WHO HAVE LOST A SIBLING:
Bereaved Parents of the USA, BPUSA, is a national non-profit that offers support to bereaved parents, grandparents, and siblings in the aftermath of a familial loss.
Compassionate Friends, founded over 40 years ago, provides personalized support to families who suffered the death of a son or a daughter, a brother or a sister, or a grandchild.
nextavenue® where grown-ups keep growing. A helpful article - Coping With the Death of Old Friends and Siblings.