Ruby Red by Kerstin Gier

1st in Ruby Red series.  Sequel is Sapphire Blue.  First published in Germany.

Gwen is 16 and lives with her mum, siblings, grandmother, aunt and cousin in an upperclass London neighborhood.  Her extended family doesn't pay much attention to her, focused on her cousin, believed to be the carrier of the time-travel gene that runs through her family and sure to show up very soon in the form of an abrupt trip to somewhere in the past.  But all is not as it seems.  Since a mathematical formula had worked out that Gwen's real birth  date was the birth date of the next time traveler, and her cousin was also born that day, Gwen's mum and (late) father secretly falsified her records to indicate Gwen was born the day before, allegedly in the hopes that she would be able to live a normal life (and since she was born at home with a midwife, no one was the wiser.

The Book of Blood and Shadow by Robin Wasserman

Nora has a pretty good life - yes, her brother is still dead and her parents are still withdrawn into their own self-absorbed worlds, but she has made a new family of sorts, with bright, charming, boy-wonder Chris and his lovely, capricious girlfriend Adriane as her best friends, and moody, quiet, scholarly Max as her boyfriend.  She also has an engrossing translation project for a local professor to strengthen her link with Chris and Max - while they work on translating the "important" parts of an ancient mystical document the professor is obsessed with, Nora translates late 16th century letters from a young woman, stepdaughter to a great magician - busy work to the professor, but more and more fascinating to Nora.  When her translation of the letters leads to a new discovery, she never expects it to end with the professor insane, Chris dead, Adriane catatonic and Max gone and branded a murder...but that's what happens.

Five Flavors of Dumb, by Antony John

Piper is a senior in high school - quiet, keeps to herself, captain of the chess team, gets good grades, the usual stuff expected from a "good girl" character in teen novels, but Piper's behavior is due in large part to her feeling isolated from her fellow students because she is deaf.  With hearing aids she can hear some things, but her hearing is not perfect, especially in crowds or when she can't also lip-read.  Her best friend, also deaf, has moved away, Piper's younger brother, a freshman, seems embarrassed by her desire for him to sign with her, and her parents have raided the college fund her deaf grandparents set up especially for Piper to attend a college for hearing impaired students - to pay for cochlear implants so her baby sister can hear and not be disabled like Piper.  She's frustrated with being different and that her parents, her dad in particular, seem to see her as broken.  In a moment of very frustrated, very un-Piper-like behavior, she challenges the lead singer of her school's Teen Battle of the Bands winner - she'll become their manager and get the band, named Dumb, a paying gig within 30 days.