Depending on your setting, it’s not unrealistic.
While I understand the concern and there are places where it would be more dangerous to try, same-sex families don’t always need the law to exist -in fact, in some countries (like France for ex) the legislation is brought on because people already do it and there’s a need for legal clarifications.
One of the parents could have adopted the son as a single parent and then live with their partner as a family -or, if applicable, parent 1 could have been pregnant with the son (either via assisted procreation or via natural means, if applicable) and then live with him and parent 2.
(Also yay for more queer representation!)
And just to add in my 2 cents it also depends on how old the kid was when they were adopted. You can still adopt someone when they’re say, 12, so there’s that too.