Are they the Study Series or the Glass Series or the Soulfinder Series or perhaps the Chronicles of Ixia?? There's been lots of confusion over the names and lots of questions coming my way over the reading order. So I'm posting the definitive AUTHOR recommended list of the books and short stories in reading order from first to last (covers are current USA print editions):
ASSASSIN STUDY (short story - http://www.harlequin.com/articlepage.html?articleId=1257&chapter=1)
POWER STUDY (short story - http://www.mariavsnyder.com/powerstudy.php)
ICE STUDY (short story - http://www.mariavsnyder.com/IceStudy.php)
NIGHT STUDY (January 26, 2016)
DAWN STUDY (forthcoming February 28, 2017)
No cover art yet!
I hope this helps :).