When making an initial purchase, please just purchase ONE time for ONE initial student. You will receive email instructions that let you self-register that initial student plus a teacher's account (if self-study) or a parent's account (if teacher-led).
Then, to add additional siblings to the same course, log in with your teacher or parent account and look for the "Add Sibling" link on your teacher's or parent's menu. Complete the transaction through that "Add Sibling" link and your existing self-registration student code will be increased to accommodate additional student(s). You can then self-register the additional students and they will be automatically linked to your existing teacher or parent account.
Please see the "Licensing and Multiple Students" section on our Conditions of Use page for licensing details on multiple siblings, unrelated students, and larger classroom environments!