While it is completely up to you what you wear for your photo shoot, I do suggest all those taking part in the photo shoot wear clothes of similar tonality. You don't necessarily have to all wear the same color (although you absolutely can), but clothing with the same general shade (but not necessarily same color) will look best in prints. Basically I just mean that it is either all light colors, all medium, or all dark. I also recommend clothing with no logos or writing on the shirts, as that all can very easily distract the eye off of what is the best part of your photos: YOU!
I have found these random compilations through various websites (some including Pinterest, of course!) and have found them helpful in visualizing color combinations for your family. If you are STILL stuck after looking through these pictures, you can also use any paint color pallete as a template. Usually the color palletes I have found on Google and Pinterest do well to coordinate colors properly. Any other questions, let me know!
And here are some color palettes to use as inspiration for picking outfits for the special Autumn Session that is coming up! Feel free to wear what you want, but I get a lot of questions on what to wear - and I like the colors on these, they are not so bright as to distract, but have enough fun and color to mesh well with pumpkins, trees, and general fall stuff!