Business involvement does not itself establish derivative-child eligibility.
Separate ownership from family eligibility
A spouse and unmarried children under 21 may generally seek derivative status, subject to applicable age-protection and other rules. Review a child approaching the age boundary separately. An adult child’s contribution to the family business does not replace the legal relationship and age requirements.
Ask counsel to assess CSPA timing using the actual petition and visa-availability dates rather than a preferred school transition date, and keep a contingency plan for a delay, since neither an investment nor a filed petition freezes a child's qualifying age by itself. Age matters more than families expect, because a child who turns twenty-one before the relevant point can fall out of the derivative class altogether; track each child's date of birth from the start rather than discovering the problem at interview.
Write down what the household needs to know that a promoter will not volunteer: which family members are covered, what happens to the derivatives if the principal's petition is denied, and what documents each person will eventually have to produce.