When you merge multiple iPhoto libraries into Aperture, what happens to duplicate photos?

My husband and I are upgrading from iPhoto to Aperture primarily to manage our large iPhoto libraries. We have stored duplicate copies of most photos we have taken together in each of our individual iPhoto libraries. We now want to merge each of our individual iPhoto libraries in an Aperture library but do not want to have duplicates of our photos in the merged Aperture library. Can anyone tell us how to merge our individual iPhoto libraries and avoid having the duplicates come across into the new Aperture library?