Adoption of Teenage Step-Son

Hello everyone! This situation is a bit unusual, and we're having a hard time finding answers. My step-father is currently wondering what his options would be to adopting my teenage brother. My step-dad had been our father figure for more than 10 years after our mother and father had gotten divorced. Both our mother and father have passed in recent years, which makes my brother an orphan of the state, and living with our step-dad ever since. We were wondering how we could go about having our step-dad adopt him? Is there any part of the situation that would make it easier, or are there any steps that we would have to take before allowing him to become his legal father? We live in Iowa if that would make a difference as well. Thank you all!