We have one kid with and one without celiac. We keep a gluten-free home, but kid #2 (non-celiac) can eat gluten whenever he is out (school lunches, etc.).
When we got everyone screened for celiac, after kid #1 was diagnosed, we also had kid #2 (and me) have the genetic test done. Although I have one of the celiac genes, kid #2 did not have any of the ones they tested for (DQ2 and DQ8). Although I know sometimes people can get celiac without these genes, it is rare, so we are assuming kid #2 is safe. If we see symptoms, we'll get him checked. Otherwise, I'm the one who is going to be checked every few years, and I have to make myself eat enough gluten ahead of time to make the test accurate.