Possible Clues:

• Goldberg and Field played them
• Women with vows
• Conical buoys
• They often have to kneel in an unsophisticated life
• Religious types, any number infiltrating student organisation
• Cloister members
• 'The ___ Story' (Audrey Hepburn movie)
• Soul sisters?
• They may be in black-and-white
• Sisters in order