Risked — Margaret Peterson Haddix

Jonah and Katherine journey to 1918 with the Romanov children in the sixth book of the New York Times bestselling The Missing series.

It's a paradox: When Jonah and Katherine find themselves on a mission to return Alexei and Anastasia Romanov to history and then save them from the Russian Revolution, they are at a loss. Because in their own time, the bones of Alexei and Anastasia have been positively identified through DNA testing. What hope do they have of saving Alexis and Anastasia's lives when the twenty-first century has proof of their deaths?