An E-2 spouse is employment-authorized incident to status and may work for any employer or start a business. Unmarried children under twenty-one hold dependent status and may study, but they cannot work and their status ends at twenty-one.
The spouse's freedom is the point people miss
Hypothetical example: the Nadeau-Osei household moves from East Ferris when one spouse buys an American enterprise, and the other assumes she will have to work in it. She does not. Employment authorization comes with E-2 spousal status itself, so she may take a job with any employer, work part-time, or open something of her own, and her earnings are hers rather than a complication for the treaty enterprise.
That flexibility is one of the practical reasons a treaty case can suit a household better than a professional route. The children's position is narrower. They may attend school, they may not work, and dependent status ends on the twenty-first birthday regardless of how the business is performing.
A household with a teenager should therefore treat that date as a planning milestone, since the alternative is usually a student route with its own admission and funding requirements and cannot be arranged in a fortnight.