Compare the project’s expected length with the practical disruption of moving the household. TD may be available for a spouse and unmarried children under 21, but it does not itself authorize employment. A short contract does not exempt family members from their own immigration documentation and procedures.
Compare joining now with joining later
Consider school arrangements, housing flexibility, benefits and the cost of a return move. These are household decisions rather than immigration eligibility tests. Ask the employer whether project completion could occur earlier than expected and build that uncertainty into commitments.
If family members join later, confirm the current evidence needed to show the principal’s TN status. Keep each person’s authorized period under review; the project schedule and household travel plans do not replace the immigration dates controlling their stay. Compare joining at the outset with joining later on the actual facts rather than on preference, since a short assignment changes the arithmetic considerably.
Set out what a full family move would cost and commit to — housing, schooling, shipping, a partner's employment interrupted — against a period that may be shorter than the disruption is worth. Hypothetical example: a household in which one partner works as a civil engineer on a long-running local project may find the cost of interrupting that career exceeds the benefit of moving together for a defined assignment. Neither answer is right in general.
What matters is that the comparison is made explicitly, and that any plan reflects TD status carrying no permission to work, so a second income would require its own separate basis.