With my chapter, we just have big and little sisters. However, we enjoy charting our "geneology". For instance, this semester I got my first little sister as well as became a great-great aunt for the second time.
Translation: My big sister had another little sister who was my "twin". She had a little sister, who had a little sister, who had another little sister initiated this semester. Right now, I'm the family "matriarch" because I'm the oldest member of my family (both in terms of age and initiation date).
During the new member program, we assign everyone in the chapter Bear Buddies each week to set aside some special time to hang out with a sister to further strengthen our bonds of sisterhood. It's a great program!