My advice to aspiring writers of fantasy trilogies or series is that each book needs two main plots. There's the 'big story', the over-arching grand plot of the entire series, and there is the complete-in-itself, one-book plot.
Juliet MarillierThird person allows a deeper exploration of the relationships between characters. We can see their misunderstandings and hear what they think about each other. We can create a more complex structure with various story threads running parallel.
Juliet Marillier