I am a photographer and this is what I would recommend.
Rather than have every one be matchy-matchy with the exact same thing on (ie.khaki pants and white shirts)decide on some specific options. You can pick and choose but only within these options. Here are some examples-
khaki, denim or black skirts/pants with solid color shirts
dressy clothes in shades of black, gray, and red
"Easter" clothes in light neutral or pastel colors
Or have each individual family match each other but be different from the other families.
*it is always cute to have the adults in neutral colors (black and white etc.) and the children all in bright, vivid, fun clothes.
If having choices is to difficult the standard that will always look good and timeless is black tops with jeans.
Feel free to visit my blog or any other websites to get inspired. bmjevents.blogspot.com