How do I adopt my dead best friend's young son?

My best friend was tragically murdered a couple of weeks ago. She was married to our mutal friend Alan together they have an infant son who is 3 months old and she has a son who is 1 and 1/2 with her ex boyfriend John. Alan has 2 daughters from a previous marriage that he doesn't see but pays child support to. It was her wish for me to adopt her oldest son Aaron with her husband Alan who is now living with me and my husband Drake. Aaron's dad wasn't involved much he would only see Aaron at mutal gatherings since Claire(my bff) and him had the same friends. John is probably going to fight us on this but my friend made it clear this is what she wanted. How would I go about doing this?