Can a sibling receive social security death benefit?

No. Domestic partnerships and civil unions are not accepted by the Social Security Administration ("SSA"), except for the purposes of name change.

The SSA does, however, accept same-sex marriages for all purposes, including the eligibility of a surviving same-sex spouse for death and Survivor benefits. (A death benefit is a small amount payable upon death for funeral expenses. A survivor benefit is a monthly stipend payable to a surviving spouse or child.)