If you're going to be mounting the bikes on the roof, that will cause a lot of drag, which equals a mileage hit... you might be better off with an Escape hybrid that you could still put the bikes inside? Or a Prius might be big enough too, I don't really know, but the back seats fold down, and it's a hatchback. If I'm wrong, somebody please correct me, after all the Civic hybrid is great, especially on the highway.

What kind of driving will you be doing?