How do Paul and Erik's parents treat the two boys differently?

In the novel Tangerine, the narrator and protagonist, Paul Fisher, often begrudges the way his parents give his brother Erik more praise and attention than they do him. His father obsesses over what Paul calls, “the Erik Fisher Football Dream.” His father goes to every one of Erik’s football practices and games, even in the pouring rain. He can name every single one of Erik’s stats, and can describe every kick he has ever made. In contrast, his father cannot even remember what position Paul plays in soccer. In one conversation they have, Paul finally calls him out on this, and his father cannot argue.  

“How many games did I play in, Dad?”

“He pulled back. “I don’t know.”

“What position did I play when I did get into a game?”

“How am I supposed to know that?”

“Ok.  Here’s one: How many field goals did Erik kick this year?”

He stared at me, and then he blinked rapidly.  “All right.  Your point is taken.”

“What’s that supposed to mean?”

“It means I understand what you’re saying. Your’e saying that I know everything about Erik’s season and nothing about yours.  You’re right, and I’m sorry.”

Paul finds this particularly frustrating because he sees Erik for who he truly is: an arrogant and cruel dictator used to getting his way. His parents are completely unaware of the cruelty Erik shows Paul and Paul’s friends. His parents never miss an opportunity to brag about Erik’s athletic prowess or their dreams for his future; they hardly ever even mention Paul. One particularly poignant example of this is when the family is invited to the home of Mr. Donnelly, a football booster from the University of Florida. They go there ready to talk only about Erik and his football achievements, and do not seem to notice when he strikes up a conversation with Paul. As they are leaving, Mr. Donnelly calls out, “It was great to meet you Erik,” and his parents just smile. When he calls out, “It was great to meet you too, Paul,”  his family “all pulled back at once, as if in group shock, as if that was the craziest thing they had ever heard.”