I am engaged, & have two children, ages 8 & 5, from a previous relationship. I have not seen or spoken to their father in years, despite my best efforts. Within the last year, we have relocated to Cobb county, GA. My fianceé wishes to legally adopt them. I am unsure how to go about this, and also whether it can be done since I can't locate their biological father to sign over his rights. What to do?

IT will be more costly to do this, since the court will require a good effort search for the bio father, and if not found, notice will have to be done by publication.
It will take a good attorney. That would be your first stop.

And welcome to Cobb County that is where I am at.

Thank you