In the media
We have found this website to be rich in relevance.
Though not specifically aimed at bereaved parents, grandparents, and siblings, it is eloquent and highly relatable.
There are many books on the subject of losing a child, grandchild, or sibling. Here are a few we like and can recommend. We'll be adding to this list.
by Anne McCracken & Mary Semel
by Barbara D. Rosof
by Roger Rosenblatt