Thank you for your post.
In your "EnrollmentData" table, you probably have a layout that has a portal into your "Members" table. In your "EnrollmentData" table, create a calculation field, "SumMembers", with the formula: Sum (Members::Marital Status)
This will sum/add the related "Members" records for each "EnrollmentData" record. Then, you can use a Summary field to sum/add the "SumMembers" field.
If you need clarification for any of the above steps, please let me know.