I have 12 inch wide subfascia on 2×12 rafter tails.  I need to install 13 inches of double stacked fascia, ie a 1 x 8 nailed low and a second 1 x 8 nail above laping the first.  I will be using Cedar boards.  What is the best nailing pattern to avoid spliting with board movement?   Nail both edges?  Nail low only on the first board and alway the second borad to hold the first?  What of second borad?

Also do you like galvanied or stainless nails?

Thanks everyone, my engineer is busy.