I read these books maybe 2 years ago. They are most likely in the fantasy genre.
Each book in the series is about a different person and the element they represent. The first one is about fire the second is about earth and the third is about water. In the first one the main character is female, and she is taken in by her father. She doesn't know that he is her father. He puts her to work as a servant. She falls in love with her brother, again not knowing she is related to him.
Another thing I remember is that each of these people, the ones that are the elements, have a familiar/animal guide. The first is a dragon, the second is a blue tiger? And the third I think is some kind of horse? Not to clear on the second and third. Each of the people have lived past lives, defending the world against some force that comes to destroy them. Some have failed some didn't. There are also people that are supposed to be their guides as well. The guide for fire dies, the guide for earth almost dies at birth but forces her soul into her twin brother. She's kind of insane, and her brother has control for the most part, but she can sometimes take over his body. I know this is all really complicated but that's what I can remember.

Thanks