Antonio's Brothers: Andrew, Eugenio, and León
"'Your blood is tied to the blood of your brothers'" Ultima tells Antonio (15.45), which is why it's such a shame that Antonio never gets to form much of a bond with them.
In his dreams and memories, Antonio views his older brothers as "Giants" who built the home in which he lives. But after they get back from the war, Antonio's old enough to see their flaws, and the brothers are old enough to know that they just don't belong at home anymore. When they're planning their escape from small-town life, Gene says about his parents, "We can't build our lives on their dreams. We're men, Andy, we're not boys any longer. We can't be tied down to old dreams" (8.100-102). We can't help but wonder if Antonio will ever reach this stage.
Somehow, we have a hunch he won't follow in their footsteps. In a way, the brothers are fallen idols and Antonio no longer trusts their power or respects their decisions, which is not all too different than how his views on God develop throughout the novel. After he knows they're leaving, Antonio wonders, "Would they always be lost to me?" (8.151). Here's hoping the answer's no.
Andrew's the one sibling that Antonio actually forms some sort of relationship with. When the three brothers return after the war, Andrew is the only one who sticks around for any length of time, and he and Antonio spend time talking on the way to school in the mornings.
But if you're thinking they've got this cool brotherly love thing going on, well, you're going to be sorely disappointed. Much to Antonio's horror, Andrew demonstrates that not all of the men in his family act honorably. When Antonio finds Andrew at Rosie's refusing to take Narciso's warning about Tenorio wanting to kill Ultima seriously, it cuts Antonio to the core:
I did not want to see anymore. I pressed my forehead against the cold wood of the porch wall and closed my eyes […] I wanted to hate Andrew for being with the bad woman, but I could not. I only felt tired, and older. (14.834-840)
Just moments after this, Tenorio kills Narciso, and Antonio can't help but hold Andrew responsible for that. And to be fair, the guy did choose being with a woman over protecting a loved one. It's not hard to argue that Andrew feels the same way about it, because soon after he leaves. We're betting he's none too pleased with himself.
The fact that Andrew was a connection for Antonio to his brothers makes it all the worse. The special bond between these two makes Andrew's fall in Antonio's eyes even greater than that of Gene and Léon. They left their family behind, but Andrew's sin and cowardice, at least in Antonio's mind, led directly to the death of Narciso—which is even worse.
Eugenio (a.k.a. Gene) and León
The Márez blood is strong with these two. Gene and León return home, take off, return home, and then take off again. They just can't stay in a small town after having seen the world while fighting in the war. Also, they're shaken by what they've seen. And since they can't shake the war, they feel like they need to just keep moving: "We could go to Denver, Frisco, hell the sky's the limit!" (8.79). Easy there, Gene.
They end up heading to Vegas, living it up, buying a car, wrecking the car, burning the car, coming home, and then leaving and taking Andrew with them. So, sure, Antonio's blood is "tied to" the blood of his brothers, but beyond that, there is not much of a connection, and they're certainly not much to look up to. Sometimes, that's just what happens when your brothers are way older than you.