Sm1smom
Super Moderator
They may never get to change it unless they say they want to adopt him. sm1smom will help us here
Just like Makiki rightly answered, nothing short of an adoption process can pave the way to their getting a GC for the kid. The adoption process itself is not even straight forward, they may need to work with an immigration lawyer to pull it off.
They cannot petition GC for him through F2A (family based GC process), for if they do, they run the risk of losing their GC (at least the principal applicant) they will be accused of fraudulently obtaining the GC by not listing him on their original application.
A major mistake on that family's part, I'm afraid!