If your father gave up all rights to you and your siblings and agreed to allow your Stepfather to adopt you.. then your bio-Dad retained zero legal obligations or rights to you at all. And paid zero child support. If all that happened then your stepfather is legally your father and your bio father is nothing other than the sperm donor. Your father and your ex-stepfather could, possibly, have come to that decision. You give us no hint of why that would have happened. However, if it did, your stepfather remains your legal Father regardless of the decisions made afterwards between him and your Mom. If it did, then there is a clear legal paper trail. And for school and such, since your legal name is not the name on your birth certificate.. that paper trail IS available. If your legal last name is the name on your birth certificate, then this entire story is all mixed up. They don't change names on birth certificates.