20 CFR §222.40

1. (a)Parent. The claimant's relationship as a parent of the employee is determined when the claimant applies for an annuity or for lump-sum payments.
2. (b)Grandchild. The claimant's relationship as a grandchild, rather than as a child, of the employee is determined when the claimant applies for lump-sum payments.
3. (c)Brother or sister. The claimant's relationship as a brother or sister of the employee is determined when the claimant applies for lump-sum payments.