4) Can you force someone to take their annual leave during their notice period?

Yes. BUT bearing in mind employees should be able to, in the first instance, choose when they holiday, it would be best practice to seek agreement first if a shutdown is in relation to Covid19.

The employment.govt.nz cites that “If an employer and employee cannot agree, an employer may direct annual leave be taken if they have first discussed this with the employee and provided 14 days’ notice before the annual leave is to be taken” so if you have been through a change process, there has been no agreement, now would be the time to implement notice commencing.