Rebellion of the Lost by Amie Kaufman and Ryan Graudin
The World Between Blinks book 2. Spoilers for book one ahead.
It opens with a report about the last book, and then Marisol finds her, during a vacation, being drawn back, except this time her brother Victor is drawn in with her. She finds herself under arrest. Meanwhile, Jake is in Australia, and Christopher and Hazel have come down, and bring him on a museum trip. A Tasmanian tiger appears -- Oz from the World -- and draws Jake back. It dumps him in the ocean, but there are people to help. They drew him back, and Marisol as well, to help with their problem, but they are shocked to realize that Marisol must have landed elsewhere.
It involves not having an arrest warrant for Victor, why the Curators came about in the first place, Marisol having to find something she doesn't know about, Great Auks and giant sloths, horrible losses of memory, T. rexes that have a complaint, and more.