As young boys grow up, having big sisters can one of the coolest things a guy could hope for. After all, big sisters can give great advice about girls and a million other things, and they can provide some insight into the world that young men desperately need. The problem is that when you're little, big sisters can flat out seem like they're from an entirely different planet. Sure, that's not always the case, but it happens a lot, and it happens to Antonio. All you need to know about Antonio's relationship with Deborah and Theresa is summed up before anything even really starts to happen in the novel:
I sat across the table from Deborah and Theresa […]. I said very little. I usually spoke very little to my two sisters. They were older than I and they were very close. They usually spent the entire day in the attic, playing dolls and giggling. I did not concern myself with those things. (1.231-236)
Despite his detachment from his sisters, Antonio's mark of manhood at the end of the novel comes when, knowing his sisters are frightened, he tells his mother to take them to their rooms. This doesn't necessarily clue the reader in to what their future relationship with their brother might be, but it does demonstrate that Antonio now sees it as his job to look after them, even though they're older.