How To Display Photographs On a Wall: Do this before making a gallery wall. Hold piece of paper on back of frame and mark with Sharpie where to put the nail-then tape back on wall and nail right through the paper!
Simplest way to coordinate extended family photos is pick one neutral color (in this case off white) and one color (blue). Then let everyone pick different shades of your main color and don't be afraid of mixing prints. (Notice the striped tee and the graphic dress print)