Official adoption of a my niece as her mother is single pare

My cousin is single divorced. She has a daughter from previous marriage, of which me and my wife traditionally adopted and raising her. Now time for her school. In my cousin divorce decree doesn't have custody arrangements layed out at all. Just 2 page divorce decleration order from court. my cousin is recently married to US citizen and she is in processing of immigrating. Now question 1. one is 'How to apply for my adopted daughters birth certificate ' second is .2. How me and my cousin workout official naming me and my wife as mother and father and get official adoption cerificates ?