The investor, a legally married spouse and unmarried children under twenty-one receive conditional permanent residence together as principal and derivatives.
Ages are measured on dates that the process itself moves
Derivative status extends to a spouse and to unmarried children under twenty-one. Because the process runs for years, a child's eligibility can be lost simply through the passage of time, and the Child Status Protection Act allows certain periods to be subtracted from a child's age depending on processing and visa availability. That calculation should be done on the family's real dates by someone competent, early, because it can influence which project and which structure the family chooses.
Adult children and parents are not derivatives and would need independent routes. One further point for a two-career household: each derivative receives permanent residence in their own right, so the nurse in this example would hold residence and could work without any further permission, unlike the dependants in the temporary categories described elsewhere on this site.