Based upon what you have written about if you can demonstrate the potential of an imminent threat as to your child there is a possibility that the court could order an injunction precluding your step-father from having any contact with your minor child.The best way to resolve the matter is to get an agreement with your "ex" stating that he will not bring your child to see your step-father. If he refuses, then you should consult with a family law attorney about seeking the restraining order you desire to ascertain the chances of success and costs.