I am not sure if you misread the laws also... I have never heard of a time limit for parental rights. Be sure about this.... I would contact the courthouse and see if you can get more info. But from what I know, every state requires you to get the father to relinquish his parental rights before they can be adopted by someone else. I do also believe you both need to be married for the children to be adopted.
Contact these people, I used them and they can answer these questions for you based on your state laws, they can also prepare the paperwork for you guys:
Child Adoption | Step Parent Adoption | Domestic Adoption
Good Luck!