Who is the main character in the book one crazy summer and how does it affect the story's plot

I have read this book, but it was a while ago, so this is all that I remember:

Delphine, aged 11, Vonetta, nine, and Fern, seven, live with their father and grandmother in Brooklyn, New York. However, the girls' father sends them to Oakland, California one summer to stay with their estranged mother, Cecile, who refers to herself as Nzilla.