A spouse and unmarried children under 21 may be included as derivatives. Adult children and other relatives are not, and each derivative's eligibility is assessed on their own facts, with a child's age handled under the applicable age-protection rules.
The household divides on age and marital status, not on intention
Derivative status reaches a spouse and unmarried children who are under 21 at the relevant time. An older child already living independently is outside the petition and would need a route of their own. Where a child is approaching 21, the age calculation is technical and should be assessed rather than assumed, because the answer can turn on processing periods that vary.
Two consequences follow for planning. The family's timetable, not the project's construction schedule, should drive when the petition is filed, since a delay that is commercially irrelevant may be decisive for a child. And on approval and immigrant visa issuance or adjustment, the family receives conditional permanent residence for two years, with Form I-829 generally filed in the ninety days before the second anniversary of obtaining conditional residence to remove those conditions.