Originally Posted by oneguyinohio
Your fiance is the one with the rights. If you adopt the child, then your rights would be equal to hers. Of course, adoption is another issue and would depend on other factors beyond your question.
As far as parenting and issues that might be involved with discipline, you will need to work those out with his mother. I have seen cases where the mother did not want the step father to do any of that.
In my family, a brother-in-law, was often in some potential trouble with law over domestic issues that involved those discipline issues...along with the entire "you're not my dad" stuff.. It was a messed up situation, and I only mention it so that you might be able to discuss with your fiance those issues before they become a problem.