While each series and book can be read as standalones, there are crossover and links within the series. If you want to start at the beginning and work your way through so you can see all the Easter eggs I've left in each books--little cameos and fun details that connect the series--here's the reading order:
Vestige of Power
Vestige of Hope
Vestige of Legacy
Vestige of Courage
Flight of a Wild Heart
Song of a Determined Heart
Falling for Zeke
Capturing Sosimo
Celebrating Tina
Crashing into Jake
Discovering Rafe
Convincing Derrick
Honoring Lena
A Rebel's Heart
A Rebel's Beacon
A Rebel's Promise
A Rebel's Trust
Wild about Denali
Wild about Violet
Wild about Rory
Wild about Emmy