Merlin's Wood: Battle of the Trees 1

Reece has always ignored Gran's wild stories about the Welsh castle he'll one day inherit. He isn't interested in his namesake, Merlin the enchanter-who-lives-backwards-in-time either. Fairytales, no. Facts, yes. Nerdy research into time travel, definitely.
Fortunately his sister Holly has paid more attention to Gran's otherworldly ramblings. When the twins are caught in a mysterious explosion and catapulted onto an interplanetary spacecraft, they'll need to know what it means to live backwards in time. Just for starters.