The investment requirement attaches to the investor, and an eligible spouse and unmarried children under 21 may accompany or follow as derivatives. That does not make them free: each person needs documents, medical examination, admissibility screening and processing fees. Any alternative route's family terms must be read from its own official instructions rather than assumed to match.
Count the household, then count again later
List everyone by birthdate and relationship, then check the list again at each stage, because eligibility is assessed when it matters, not when the plan was drafted. A child who turns 21 during a long wait raises age-protection questions that depend on the specific facts and dates. Marriages, births and a dependant's own immigration history can all change the household total between filing and interview.
Add one further habit to that recount: record who was asked and when, because household composition is checked against facts at particular moments rather than against the family's intentions. A birth, a marriage, a separation, a child's changed circumstances, a dependant's own immigration history coming to light — each can alter the position, and each tends to be mentioned casually months after it happens. Set a recurring point at which someone asks the household directly whether anything has changed.
Hypothetical example: a family reviews its list at three scheduled points across a long wait, and the second of those reviews surfaces a change in an adult child's circumstances that nobody had thought to mention because it did not seem like an immigration matter.