The Wakefield Twins
Who can forget Elizabeth and Jessica of Sweet Valley? The series that ‘grew up’ with us. Im pretty sure we all started from reading the Sweet Valley Kids series then we moved to Sweet Valley Twins..and until we were old enough to read the Sweet Valley University.
For a list of the different titles for each series, check out http://thebookliberationproject.wordpress.com/collections-backlists/sweet-valley-created-by-francine-pascal/