Work authorization follows status, not the file's progress. A legally married spouse admitted in qualifying E status is generally employment-authorized incident to that status; a spouse currently holding some other status must rely on whatever that status allows. Check the I-94 annotation or E-2S evidence before anyone starts or changes a job.
Map the household's income across the transition
If family income currently depends on the existing business or on a spouse's job, work out what happens during the change and whether the household can absorb a gap. Unmarried children under 21 may accompany as dependents but receive no employment authorization from that status. Each person has their own eligibility and process, so avoid booking a move around one assumed date, and remember that non-marginality is judged on the enterprise, not on the family's other income.
Prepare one activity plan per relative, recording relationship, age, intended E status, admission evidence, schooling, and any compensated or operational role. Identify the treaty-national investor, confirm that qualifying nationals own at least 50 percent of the enterprise, and document how the principal will develop and direct it through ownership or operational control. The spouse's own nationality does not matter for derivative status, but a spouse who is a Canadian citizen could also qualify as an E-2 employee in a separate application if that ever became useful.