Reading Order - Greek Mythology books

All of these books are set in the same world of Olympus and feature the twelve Olympian Gods and their realms. 
The Immortality Trials and Olympus Academy are set first (and chronologically at the same time) but you don't have to have read them to enjoy the others, they all standalone.
The Immortality Trials is a retelling of the twelve labors of Hercules and each of the twelve trials takes place in a different God's realm, so I recommend reading this series first if you want to get a good feel for the world of Olympus and meet all the Gods. 
Please note that The Immortality Trials is the only one of my series that is in third-person, and it has multiple point-of-view characters. There is only a tiny bit of swearing and no on-page steamy scenes although it is definitely romance. It is classed as Young Adult. 
Olympus Academy is set predominantly in Poseidon's realm, and should ideally be read second, but can be read first.
Please note that Olympus Academy contains no swearing or steam at all and is suitable for 12+.
The Hades Trials is set later and although there are references to events from the previous two series and features some characters, there are no really big spoilers. If you are only into more adult books with steam - start here!
Please note that The Hades Trials contains steamy scenes (especially the last book) and some swearing and is only suitable for adults.
The Ares Trials follows on directly from the Hades Trials. It does not have any big spoilers but makes up part of an interconnected series plot that will make more sense if you have read The Hades Trials.
Please note that The Ares Trials contains steamy scenes and some swearing and is only suitable for adults.