Family timing should generally wait until the duty breakdown and degree match are confirmed, since a role that turns out not to fit the biologist category may require reconsidering the route entirely. Dependents would travel without independent work authorization under a dependent status.
Hold major decisions until the category question is settled
Because this scenario carries real uncertainty about whether the role fits the biologist category as structured, avoid firm household commitments until that question is resolved. If the research appointment has a defined project length, factor that into whether a full household move makes sense versus a more limited arrangement while the category question and any renewal prospects become clearer. Hold the household decisions until the duty breakdown and the degree comparison are both resolved, because a position that turns out not to fit the category changes the route rather than the timetable.
Dependants travel in a status carrying no independent work authorisation, so a spouse who needs to earn requires a separate assessment on their own facts. Where the appointment has a defined project length, weigh a full household move against a more limited arrangement until renewal prospects are clearer. Grant-funded posts deserve particular attention, since the end of a funding period arrives sooner than families expect and rarely moves to suit anyone.
Write the decision down with its reasons.