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)