Sometimes his overt Mormonism bleeds through into the story, but most of the time you can overlook it.
The Homecoming saga is pretty good.
Even though it is overtly the book of Mormon put in Scifi cloth.
Still pretty good though.
I wanted to punch babies with what he did at the start of the forth book, or more accurately the end of the third.
Even though I know why he did it
And to the OP:
My understanding is that the movie is primarily based on Ender's Game, with some elements drawn from Ender's Shadow.
Which take place chronologically at the same time.
If you want to insist on reading the first books to the movie, you would be fine reading Ender's Game and then Shadow.
FWIW, here is my revised chronological order of the books if you are interested (I removed shorter pieces that are better off left reading till after, and which reek of money making and quite possibly were ghostwritten):
Shadow of the Hegemon
Shadow of the Giant
Ender in Exile (You can choose to omit this as well).
Speaker for the Dead
Shadows in Flight
Children of the Mind
Although there is a LOT to be said about reading the Ender Quartlet first (As it was published), and then going back and read the rest in whatever order you'd like.