I think it is hard to beat a classic beautiful old brasserie for a group of diverse ages and tastes. Some of the better ones are Terminus Nord, Gallopin, Vaudeville, Mollard, Marty and Thoumieux. These are spread over Paris and one should be near you and they are open most of the time.
There is a croissant place on Champs-Elysees across from the Marriott. Really good. Breakfast for two (croissant and butter and jam and coffee for me and my young bride) was about $35.00 in March 2008. Could be a bit less now with the dollar strengthening some.
Two seafood places also on Champs-Elysees, one of which specializes in mussels, are also exceptional. Sorry, neither of us can remember either name. But you can find them. If you do, try the mussels with Roquefort cheese. Amazing.