Antagonist
Character Role Analysis
One of Those Group Efforts
If we really wanted to oversimplify it, we'd say the antagonist is the bad guy, the person who's always thwarting the protagonist and keeping her from getting what she wants. But there's not really one character who does this in hush. The problem is the situation, which is that Toswiah/Evie's family has to enter witness protection after her father chooses to testify against two fellow cops.
Granted, a lot of potential bad guys contribute to the situation: Officers Dennis and Randall, Joseph Randall, whoever fires shots through the Greens' dining room window. However, none of these characters spends enough time on the page to develop into a true antagonist, and the story is about how Toswiah/Evie copes with the situation, not about how she deals with a particular character.