you do this with the Manage Relational table behavior.
the manage relational table behavior will update your linking table that creates the many to many relationship of the student to parent / caregiver
you would need to create the student insert. Then create a record to pull all of the parents that should be listed to select from
using a repeat region, you can display each parent as a checkbox.
The add the manage relational table behavior to update the lining table.
this post has some details for working with the manage relational table behavior: