20 CFR § 222.40 - When determinations of relationship are made for parent, grandchild, brother or sister.

(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.

(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.

(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.