The E-2 spouse is employment-authorized incident to status and may work in the family business or elsewhere. Children under 21 hold E-2 dependant status, may study, cannot work, and lose derivative status at 21, which needs a plan for a seasonal business that runs for years.
Plan the children's ages against the length of the business
E-2 status can be renewed for as long as the enterprise continues to qualify, which makes it a long-horizon status for a family, and the children's ages are the first thing that changes. A child who is 17 at the first visa will turn 21 during a normal run of extensions and must then have their own status, whether as a student, a worker or through some other route, or return to Canada. Record each child's birth date and plan the years in which that transition falls.
The spouse's position is simpler: employment authorization incident to status means they can take a job with another employer or run part of the enterprise. Keep proof of the marriage and each child's birth ready for the consular interview, and remember that E-2 gives the family no path to permanent residence on its own; if that is the goal, it should be discussed as a separate question.