Other claimants will be considered to have the relationships to the employee shown below for lump-sum payment purposes:

(a) Grandchildren. A grandchild is a separate class of beneficiary to be considered for lump-sum payments and is not a child of the employee; he or she is a child of the employee's son or daughter as determined under State law. A stepgrandchild is not included in this class of beneficiary.

(b) Brother or Sister. “Brother” or “Sister” means a full brother or sister or a half brother or half sister, but not a stepbrother or stepsister.