This comic's comments
On LiveJournal, Kyleen66 commented, I thought Caius was Stephanus' son? But he is his brother? And wasn't he supposed to be freed when he gets to be a certain age?
Caius called Iusta "sister," and Stephanus' will arranged for Caius to be freed if he had already reached the age of thirty. I did change the relationship, though. Not only does this make it more complicated (always more fun), it's more likely, I think, that Stephanus wouldn't have just made arrangements to free Caius no matter how young Caius was. That's my thinking, anyway.