If the account is to be paid to the participant's parent or parents under § 1651.2(a)(4), the following rules apply:

(a) Amount. If both parents are alive at the time of the participant's death, each parent will be separately paid fifty percent of the account. If only one parent is alive at the time of the participant's death, he or she will receive the entire account balance.

(b) Step-parent. A step-parent is not considered a parent unless the step-parent adopted the participant.