Each investor has their own application and their own family members. A spouse admitted in E-2 status is employment-authorized incident to that status; children admitted as derivatives may attend school but are not authorized to work on that basis.
Two investors means two files, not one
Hypothetical example: the two contractors assume that one application covers the venture and everyone attached to it. It does not. Each individual seeking status applies on their own facts, and each must satisfy the requirements, including developing and directing the enterprise.
That is worth thinking about carefully where two people share the investor role, because both need a defensible description of their authority and their contribution. Each investor's spouse is employment-authorized once admitted in E-2 status, and each family's children may attend school. Derivative eligibility ends at twenty-one.
Confirm every person's citizenship individually. And note that E-2 status provides no direct route to permanent residence, so families expecting to settle indefinitely should understand that limitation before money is committed.