This is a complicated question!
Let's start with Antigone. Which "unwritten laws" does she defend? Well, several, but one of the big ones is the unwritten law to bury the dead, especially your relatives. Creon forbids this, but Antigone goes against his orders (and thus effectively breaking the law of the city) and buries her brother. She prioritizes the unwritten cultural/religious/moral law about burial over the secular laws of the city and obedience to the king.
For Socrates, we want to look in particular at the Crito. There, Socrates argues that in virtue of being a citizen and accepting the benefits of citizenship and living in the city, you agree to follow the laws in a kind of implicit contract. Socrates says that this implicit contract is very important, binding, and gives it as the reason why he doesn't escape and instead submits to the death sentence he was given in Apology (for corrupting the youth, inventing new gods, and not believing in the gods of the city).
So Socrates is going to say that Antigone violates that implicit contract she has with her Polis by virtue of being a citizen. The real question is whether the force of the contract is stronger or weaker than the cultural/religious/moral requirements of her duty to her dead brother! Weighing these competing demands is the real heart of the issue, and each of the characters/people mentioned is going to have a different perspective on it.
I hope that helps!