The Eighth Hell - Sisters of the Storm, #3

None who have gone to the Shingora ever returned . until now. Despite the danger, the trade guilds sent an expedition to the Shingora, believing the island was a wellspring of natural resources. Only one man returned, as a gibbering madman. Now the guilds are sending a new expedition, three hundred strong and armed for war, to search for any survivors . but on the Shingora, everything kills. Among the expedition are Aleena, gifted by the gods in war, and her sister Baezha, gifted by the gods in magic.
But while battling all the Shingora's perils, a traitor threatens the company from within. The sisters will be tested as they've never been tested before . and even those Chosen by the gods have their breaking point. Though listed as book 3 in a series, this is a stand-alone novel.