Blue window / Adina Rishe Gewirtz.

Enhanced descriptions from Syndetics:

Five siblings fall through time and space into a strange, unkind world -- their arrival mysteriously foretold -- and land in the center of an epic civil struggle in a country where many citizens have given themselves over to their primal fears and animal passions at the urging of a power-hungry demagogue.

When siblings Susan, Max, Nell, Kate, and Jean tumble one by one through a glowing cobalt window, they find themselves outside their cozy home -- and in a completely unfamiliar world where everything looks wrong and nothing makes sense. Soon, an ancient prophecy leads them into battle with mysterious forces that threaten to break the siblings apart even as they try desperately to remain united and find their way home. Thirteen-year-old twins Max and Susan and their younger siblings take turns narrating the events of their story in unique perspectives as each of the children tries to comprehend their stunning predicament -- and their extraordinary new powers -- in his or her own way. From acclaimed author Adina Rishe Gewirtz comes a riveting novel in the vein of C. S. Lewis and E. Nesbit, full of nuanced questions about morality, family, and the meaning of home.