Anyone But You by Lara M. Zeises

Family, it turned out, was something you really could choose yourself. Seattle should know. Critter and Jesse have been close to Sea since her dad moved in with their mother. Closer still since he took off six years ago and Layla decided to raise Sea as one of her own. It's a decision none of them regrets, especially not Critter. He's more than a brother- he's Seattle's best friend.
Now it's vacation, and Seattle and Critter are stoop sitters, at least until summer school starts in July. It beats working, like Jesse, or worse, studying, like Layla wants them to. It's too hot for Seattle to be on her skateboard- too hot even for Critter to be scamming in girls. But Sea comes up with a plan for them to bluff their way into the ritzy swimming pool the next town over. Big mistake.
Soon Critter's got his heart set on a Penn Acres princess, while Seattle is trying hard not to fall for a skater boy on the rebound. For the first time in a long while, they can talk to anyone but each other. Then Seattle's dad shows up unexpectedly, and the way of life Critter and Seattle have always known begins to change even more..
With this powerful novel of two voices, Lara M. Zeises takes a fresh, hard look at what it means to be a family.