Good evening dear colleague,
I think it would be much easier for you and your students if you use the context in the Action Pack 9. Because, in this series we have a contextualized grammar in each module.
Just after studying the context and discussing the material with the students, work on the modals. After that, you can use a simple worksheet to enhance the understanding of using must, mustn �t and needn �t.
It �s good to use real situations with students in the classroom while explaining them.
Hope this will help you.