If you like the look of your birthstone and your spouse's, one option is to pick a "his" and "hers" scheme. Use Dad's stone for the boys, and Mom's stone for the girls. Birthstones are a secular, cultural tradition, and we're all about freedom, right?
The main idea with Solomon's Bow is the symbolism. The parents are represented by the bow, and they motivate and propel the children.
In my original design, I used opals (my birthstone) and diamonds (hers)(very small ones) for Katrina and our daughter. The concept of birthstones is widespread in our culture: pretty much everyone "gets" birthstones. When I decided to offer the bow as a production item, I moved to birthstones, but if you want something a bit different, just ask!