The two aren’t related at all the queen had an affair with another man and Joffrey just happened to look like the queen. Edward (? I think that’s his name, the blond guy) is the kings actual biological child that he had with a commoner named rose(? I think that’s her name)
But it’s true that they do get together I remember reading somewhere that Edward takes Joffrey and they have some sort of relationship in that manner

Hey so I’m just at the earlier chapters rn and I’m just wondering about if there’s incest?? Like aren’t the MC and blonde guy related in a way?? Im just not rlly comfortable with reading allat and i dont wanna waste my time