These resources are specifically and explicitly for sibling loss. Most if not all the books I recommend on other pages for children and adults are helpful for other losses.
For Adults Who Have Lost a Sibling
Donnelly, Katherine Fair. Recovering from the Loss of a Sibling
Horsley, Heidi (lost a brother at age of 20 years). https://www.opentohope.com
Kincaid, Jamaica. My Brother
Linn-Gunst, Michelle. Do They Have Bad Days in Heaven? Surviving the Suicide Loss of a Brother or Sister.
Mansbach, Adam. I Had a Brother Once. A Poem. A Memoir
Wolfert, Alan. Healing the Adult Sibling's Heart.
Wray, TJ. Surviving The Death of a Sibling. Living Through Grief When an Adult Brother or Sister Dies.
For Children and Teens who have lost a sibling
Abbott, Tony. Denis Ever After
Appelt, Kathy. Maybe a Fox
Bishop, Jenn. The Distance to Home.
Carey, Janet Lee. Wenny Has Wings
Condie, Ally. Summerlost
Daniels, Natasha. The Grief Rock.
Doan, Autumn. I have a Brother in Heaven.
Lecourrege, Megan. My Sibling Still. (Miscarriage, Stillbirth, and Infant Death)
Mir, Saira. Always Sisters (pregnancy loss)
Rissi, Anica. Wishing Season
Thesman, Jean. Calling the Swan
Warga, Jasmine. The Shape of Thunder (school shooting)