We've done several family pics over the years, some outfits we wore are...
1) Girls and I wore black with white collars, DH in black suit and white shirt.
2) Adults wore solid red shirts, kids wore matching prints with red in them.
3) Denim shirts with jeans.
4) Red, white & blue. I think DH had on a solid shirt, I wore white with blue stars. One DD wore a sailor type dress in those colors, other DD had a white shirt with a heart in the middle in those colors.
I also did a picture with myself and the girls (as a present for DH) and we all wore white one time and red the other.
I like the suggestion of white shirts with blue jeans, unless you don't think that is dressy enough for a church directory, then you could go with the khaki's as someone else suggested. I was on our church directory committee 2 years ago, and there was a combination of all styles.