Can a person adopt if they are a convicted drug felon?

My brother recently got custody of his biological son due to the death of the childs mother. He would like to adopt the child's brother from another "unknown" man. The children were/are under legal guardianship of their maternal grandmother which would like nothing to do with the children. Both children have been living with my brother for a little over a month now. Problem is, my brother is a convicted drug felon that has served time years ago. He has since maintained a job and home for more than three years. What are the odds of him getting custody of his son's brother as so they are not separated?