When the $$ is in one pot, it's easy to think since the family is FI, and therefore both folks are FI, but since about 50% of marriages end in divorce, the reality is they are not both FI if divorce happens..
If the family unit is FI, I think you can consider both spouses FI. Sure, things could happen to change that (divorce, major lawsuit, market crashes, etc), but I don't think you can say they aren't FI at the present time just because one of these future events "might" happen.