Emma was the wife. Annie, died at 10 years of age, his daughter.
Evidently, it was that event that turned him away from God. She was 10. Virtually no one writes about this aspect of what 'drove' him.
Logical fallacy of origins here. It doesn't matter whether Darwin's ideas about evolution came from a questioning of Christian beliefs or from some other source. They are true or not on their own merits.