I have read this entire series, and as nearly in order as I have been able to figure it out. That is not really easy to do, as the author's website does not list all the books. It is not always easy to follow the book lists at the end of all of the books. There are four books that Bookmate does not have at this time. I bought them on Apple's iBooks. They are, The Fate of Ten, United as One, I Am Number Four: The Lost Files: Last Defense, and I am Number Four: The Lost Files: Hunt for the Garde.
This series kept me up too late on too many nights, as the characters are well developed, and the plot never drags. I look forward to re-reading it in the future.
I cannot recomend this series highly enough to people attracted to this genre! Congratulations to the author!