Legal Question in Family Law in Alabama

He doesn't. The prior court proceedings terminated the legal rights of the biological father, and the adoption makes the stepfather the legal father of the children. Unless the biological father could prove some kind of fraud in the adoption process that would rise to the level of voiding the proceedings, the biological father is out of luck.

Unlike child custody orders which are always subject to modification, an adoption is permanent. If this was a legitimate adoption, the biological father has no legal authority to challenge the stepfather's authority. Perhaps as the children get older they will want to seek out the biological father to get to know him, but until then there is not much that he can do.