Possible Clues:

• One's installed in street by popular demand
• Demand sister gets in makeshift container
• Persistently demand
• To maintain central core of gas mains is tricky
• First of the women & each respective sibling having left, identical girls carry on being demanding
• Demand in relation to 50% off
• Demand member of family stops within short time
• Those elected first to make demand
• Emphasise sin must be cast out -- it's wrong
• Don't back down