No. Derivatives are the spouse and unmarried children under 21, and stepchildren qualify only if the marriage occurred before the child turned 18. A 22-year-old is an adult and would need his own route; the younger children can be included.
List who qualifies before the family plans around the move
Hypothetical example: the contractor and his wife have two children of nine and thirteen together, and her son from a previous relationship is 22. The two younger children are derivatives and will receive conditional permanent residence with their parents, subject to the Child Status Protection Act calculation if processing runs long, which for children this young is unlikely to matter. The stepson is outside the category twice over: he is older than 21, and step-relationships are recognized only where the marriage took place before the child's eighteenth birthday, which would need to be checked against the marriage date even if he were younger.
He can visit, apply for a student status, or later be sponsored as the adult child of a permanent resident, each with its own timeline. The family should decide whether he will remain in Québec for his studies and how that affects the parents' own move, since the investor and spouse need to be admitted to the United States to activate their conditional residence. Every derivative also needs the same admissibility review as the principal.