BiKE tour.. the girls will love it.. and so will you ( if they are over 16 let them go on their own if you dont want to .. but the rides are easy and mostly flat so even though I hadnt been on a bike in decades I had no problem )..
Fat Tire bike tours.. does a day and night tour.. the night tour includes a boat ride too.
Actually .. having taken teens to Paris myself I can tell you the best thing you can do is GET THEM INVOLVED with the planning.. starting at age 11 I had my kids contribute to their visits by telling them THEY had to do some research and find at least three things they wanted to do and see.
They all come up with the usual "Eiffel Tower" stuff.. however they can and do find things that may interest them more than you .. but its fair play.. you drag them to a museum and they drag you somewhere you might not have gone.. perfect example for me was when my son said we had to visit the Catacombs.. he loved it ..