Adoption question

So my husband wants to adopt his ex gfs little girl, he’s raised her since she was born, but she does have her biological dad in the picture again.. how would he go about doing that? Does he just need the moms permission or both parents?

Update: the real dad isn’t even on the birth certificate and my husband wants to just give the little girl his last name? Is there an easier way to do this? I know this is very complicating and crazy, but he’s really stuck on this subject.