A qualifying E-2 spouse is employment-authorized incident to status under current policy, so a spouse may generally work, including in the enterprise. That is separate from the marginality question, and a family's own wages are not what shows the business is more than a source of household income.
Family employment does not answer the marginality question
It is common for both spouses to work in a small business they have bought, and nothing about the category forbids it. The point to keep clear is that the income the enterprise provides to the investor's own household is exactly the income that does not demonstrate non-marginality. The evidence that does is employment of others, or income beyond what the family needs, or a documented capacity to reach that within a reasonable period. Children accompanying the family in dependent status may attend school and are not employment-authorized. If a spouse would rather work outside the business, confirm the notation on the arrival record at admission, since that is what a prospective employer will ask to see.
Hypothetical example: Kenji, a theatre-lighting supplier, assumes every family member can work once the business opens. The family review should distinguish an E spouse from an E child: a qualifying spouse is employment-authorized incident to status, while a child may study but does not receive the same work permission and ages out at twenty-one. Marriage, birth and passport records must support each derivative application. Kenji’s own eligibility still depends on treaty nationality, qualifying enterprise ownership, substantial funds committed at risk, a real non-marginal operation and his direction of the business. Those enterprise facts should be settled before anyone relies on a derivative benefit for employment or school planning.