The E-2 spouse is employment-authorized incident to status and may work in the family business, but guiding paying clients also requires whatever state guide licence applies. Children under 21 may study only and cannot crew for pay.
Immigration authorization and the state licence are separate permissions
An E-2 spouse admitted with a properly annotated I-94 may work for any employer, including the outfitter the couple owns, without applying for a separate document. Depending on the destination state's rules, guiding may require a guide licence, first-aid certification or a boat-operator credential; those permissions come from the state, not immigration authorities. The spouse therefore has two steps, not one.
The couple's children hold E-2 dependent status until age 21, may attend school, and may not be employed, which includes helping on the boats for wages or tips. A seventeen-year-old cleaning fish at the dock for pay is unauthorized employment. When a child turns 21, dependent status ends, and the child must qualify independently, for example as a student, or leave.
Build the staffing plan on hired U.S. guides plus the two adults, and do not assign the children unpaid work that the business would ordinarily give to paid staff.