Lost In Oz, a trilogy by Joshua Dudley. While having no relation to the Lost In Oz TV pilot by David Hayter, or the original movie idea by Tim Burton, this book was concieved as an original idea, but still catering to fans of the original Oz book series.
First set in modern day, Joshua(named after the author), his twin sister Tamara, along with their schoolfriends Tommy and Laura are suprised to find themselves hurled to Oz. Once there, they run into Dorothy who has just befriended Scarecrow, Tin Man, and Lion. They are all on their way to see the Wizard, so Jousha and his crew have not only travelled to another realm, but gone back in time to when Dorothy first arrived in Oz in 1899. Plus, their initlal encounter with her has caused a whole new timeline to occur. Joshua and Tamara have an arguement, which causes the two girls to go stalking after Dorothy so they can find a way home, while Joshua and Tommy get left behind. Joshua can keep up with them though because his copy of the actual Wizard Of Oz book is now narrating what is going in Oz similar to Glinda's Great Book of Records. After encountering some flesh-eating merfolk(in Oz?), Joshua and Tommy meet Jack Pumpkinhead who was apparently sent back in time from some point of the original timeline that still exists, and tells Joshua he is part of some cryptic prophecy. Tamara and Laura get kidnapped by Bastinda, the Wicked Witch of the West, who Joshua and Tommy find out has been fronting as the actual Wizard as well. They learn of the girls' abduction and head out to the Witch's castle, only to run into another time-displaced character, Scraps, who is unfortunately torn apart by the flying monkeys. They are also captured while trying to save the girls, where Joshua meets Oscar Diggs(the actual Wizard). He reveals to Joshua that Bastinda was his wife from America who came to Oz with him, and she gained magical powers along with her sister to become the Wicked Witches. This isn't even more shocking as the fact that Joshua is their son, who was sent to America as a child, and his "sister" Tamara with her family were enchanted to thinking he was her twin. Oscar then just disitegragtes, leaving Joshua to reconsider Jack's prophecy. Tamara frees Joshua after Dorothy melts Bastinda. The foursome then decide to just tail Dorothy and her friends to Glinda's palace and try to catch a ride home from her when she "clicks her heels three times". However, they end up in their time about two years after they first left and have been presumed missing. They end up getting admitted into a asylum, where they meet a young girl named Alice chasing a rabbit. Now in case your wondering, yes this is the Alice from Wonderland, which crosses-over in the next volume of the series, Rise Of The Dark Wizard.
The second book is now out, with the third one, Temple Of The Deadly Desert, due out early next year. Currently, there are copies for sale through most regular sellers like Amazon and Barnes & Noble. It's also available on Lulu along with a Special Edition available only for download. The book itself is in a regular paperback edition as well as a deluxe paperback.