After one week on the ship, what does Mother have Há's older brother do for the children on board?

Há's brother works on helping the children learn to speak English.

About a third of the way into the story, in the section titled "Routine," we learn that Há and her family have been on the ship for a week. It's a tough situation: there's just barely enough food and water to keep them all alive, and it's incredibly boring.

Há explains that her mom doesn't "allow idle children, hers or anyone else's." She means that Mother hates to see kids wasting their time doing nothing, even if it's not even her own kids.

So: 

"Brother Quang begins English lessons."

The narrator doesn't tell us straightforwardly, but we can assume that it's Mother who is having Quang give the English lessons to all the kids on board. (Why else would she tell us first that Mother hates to see children being idle?)

The lessons are probably useful for the kids, who will have to assimilate quickly into the English-speaking world, not to mention they are probably also a welcome distraction. Há, however, is quickly bored by these lessons. She wishes she could just learn the easy stuff, like how to say "How are you?" or "This is a pen." Instead, Brother Quang insists on reminding the children that entering a new country without knowledge of the language is shameful.