I herewith submit the answer.
The consent is given by your stepdad cannot be changed by the employer. If your stepdad changed the beneficiaries of your mother and step sister to YOUR MOTHER ALONE will only be acceptable, when it is signed as last form. The employer has no such right to change the beneficiaries. Any changes must be done by the employee only. So the latest form signed by your stepdad is acceptable. Therefore find out latest form.