Merging iTunes libraries, Keeping separate playlists?

In our household we have 3 differnt iTunes libraries, Mine, my Dads, and my Mums. All of these playlists differ to some degree (although there is some overlap with duplicates) and are all stored on separate computer and synced to separate iPods and iPhones. My Dads is stored on his work laptop, Mine on my mac and my Mothers on the main home PC. Since we recently started using Airfoil to stream our music around the house I wanted to merge the three libraries into one, However I wanted to keep each library separate in a playlist, i.e. we could shuffle through everyone's music by playing the whole library or just an individuals by selecting the specific playlist. I know how to merge them and have a rough idea on how to keep each library in a separate playlist, the problem is getting rid of the duplicates, I know that there is the 'Delete Duplicates' item in the iTunes menu bar, but when I delete one version of the file, it will be removed from the playlist it was in, however the version that was not deleted will still exsist in the other playlist. (I hope that makes sense, Basically if two of us have a copy of for example 'Alive and Kicking' By Simple Minds, and using the Find Duplicated section I delete the one that was in my library, I would lose it from my playlist but the other person that had it would not lose it from there's). Is there anyway around this by somehow merging both songs into one so both playlists pull from the same file and only one version exsists in the library.

Thanks

Cameron