Yes. The spouse of an E-2 principal is admitted in E-2 dependant status and is authorized to work incident to that status, in the family business or anywhere else. Children may study but have no work authorization and lose dependant status at 21.
One principal, one working spouse, no working children
Hypothetical example: the wife has run the parts counter and bookkeeping in South Frontenac for years and intends to do the same in New York, while the husband takes the principal investor role. She does not need her own E-2 case or a separate work card; her dependant status carries employment authorization from admission, and the shop can put her on payroll. What she should carry is proof of the marriage and her own Canadian passport, since the dependant's nationality is not required to match the treaty but is still recorded.
Their nineteen-year-old son, who has helped in the shop since school, may accompany them and study but cannot be employed, paid or unpaid, and his dependant status ends when he turns 21. If he wants to work in the business he needs a category of his own, and a small dealership is unlikely to support a second E-2 investor. Plan the staffing around the two adults and treat the son's involvement as a separate question to be answered before he turns 21.