Fix the immigration steps first, since they gate everything else, then place school enrolment, the departure date and the start of the spouse's job search behind them. Searching can begin earlier than working does, provided nobody treats an interview timeline as a status timeline.
Build the plan around dependencies, not hopes
The dependants' timing depends on the principal's case, which depends on the company producing evidence. Every link can slip. Identify which decisions are reversible, such as a delayed lease or a deferred school start, and which are not, such as resigning from current employment.
Keep the irreversible ones as late as possible, and agree a checkpoint where the family reassesses if a defined milestone has not been reached. Distinguish clearly between the two activities that are easy to conflate: searching for work and beginning it. A spouse can research the market, speak to recruiters and attend interviews well before any status question is settled, provided nobody treats an interview timeline as a status timeline or accepts a start date that assumes one.
Where an offer arrives before the family travels, that is a good problem, and the right response is to tell counsel and the employer at the same time rather than agreeing a date and asking afterwards whether it works.