Grade School Invaders from Beyond the Stars - William J. Smith - Bog

William, Oscar, Nancy and Carol Anne are typical siblings from a typical, middle-class, every-day family named the Smiths who, like most siblings, have times when they get along and times when they argue and fight. When they discover a plot about aliens disguised as students in their schools being part of an advanced team of alien invaders, they must ban together to fight to save their lives and the world with the help of these mysterious "men in black", that they've all heard so much about.