Jenna Bush Hager and Barbara Pierce Bush are known everywhere as the children and grandchildren of two U.S. presidents, but talking to them, it's immediately clear that they are, as the title of their new book says, sisters first. Jenna calls Barbara "sissy"—short for "sister"—and while it's also immediately obvious that they're very different people, they're deeply in sync. "One of the themes of our lives is, we have this person who's given us a voice or listened to our voice. We're twins, so in some ways we've spoken for each other," says Jenna, who is a correspondent on the Today show, has written two children's books, and has previously appeared at the festival, which was founded by her mother.

"We had always daydreamed of writing a book together, but it was always an idea in our heads that we just liked to talk about," says Barbara, who is the CEO and cofounder of Global Health Corps, an organization that supports global health leaders. "We've always known how lucky we are to have had the life we've had," she continues.

The idea for a book gathered steam when Jenna was pregnant with her second daughter. "We wanted Mila to get excited for her new little sister, which got us talking at the time about a book about being sisters," says Barbara. Around the 2016 campaign and election, the idea went from daydream to plan.

"It was so clear, with the campaign and the broader language around women, how important it is to build women up right now," says Barbara. The sisters see the book as a personal way to combat the reductive effect of boiling everything down to tweets and Facebook posts. "It was important to us to write about the people that we love who are public figures and show more sides to them to make them more complete people. That is so much of what is missing right now in the dialogue around issues in our country. It seems like we're just seeing people for three attributes of themselves rather than who they truly are as a full human being," Barbara continues.

"We're not talking about political parties," Jenna adds. "We're talking about decency and kindness and humility. Our grandpa never talked about himself. He still never talks about himself. I learned things about him through reading biographies because he would never brag or show off, and people may not know that about him."

While Sisters First is by no means a political book, it speaks deeply to the strength these two women draw from each other and their close bond with the members of their famous family. "Things feel very divisive right now, and politics feel very different than when we were growing up," says Barbara. "We've always had someone that has had our back and thought that we were enough and supported us in the decisions we were making and the risks we were talking," she continues. "We both realized how grateful we are."