The primary benefit of having multiple pay-monthly lines on the same billing account is the ability to share data between them, providing none are "No Frills" plans.
You would need to conduct a legal change of ownership to merge the accounts - follow the advice under "transfer to a friend, colleague or family member" on https://ee.co.uk/help/profile/manage/change-my-account-in-the-case-of-a-life-event
