The Due Date (or DateDue) should be a settable property of the enrollments API endpoint.
Due Dates are what our Administrator use to drive compliance and there's not an efficient way for them to add different due dates for different groups of students in bulk. Utilizing the API gives us a workaround until setting due dates on bulk enrollments becomes a thing (fingers crossed).
Due dates are tied to the rules established at the course level. In the course edit within the administration module, you can set the due date as a function of enrollment date (e.g. +14 days) which will apply to all learners enrolling in this course. Please let us know if that satifies this requirement.