I know that teens over 18 receive their own invitation even if they still live at home but do you need to send multiple save the dates to the same household?
I don't think so. If you list the family name on the STD, you should be set. They would probably keep only one anyway. Also, if the teen is still in highschool, I include them on the parent's invite. Why spend the extra postage? In my FI family, they insisted that ANYONE living at home with their parents can be included on a household invite...so I took their advice and saved the money. I guess it depends how formal you want to be or how people in your circle normally do things.
Re: Save the Date Question