Mavericks Series by Craig Alanson

The human soldiers stranded on the planet Paradise have been recruited into an Alien Legion, to do the dirty jobs that the high-tech species won't do. Their first mission is to kick the enemy off a backwater planet no one cares about. It's a simple assignment, except everyone has a hidden agenda, and the planet could become a deathtrap.

The Alien Legion has a new mission, and this time, they are working for the enemy. Also against the enemy. Like every operation that Emily Perkins plans, it’s complicated. But plans require good intel, and when the plan falls apart, the Mavericks are in Freefall…