Unfortunately no, there is no way to upgrade from a single user license to a family license. In addition, is the disc that you're talking about from the retail box for iLife (white) or from the discs that came with your MBP(grey)? If they're the grey discs then I'm pretty sure they're tied to that specific computer and won't work on other Macs unless they're the exact same model.
Also, just a hint, before you post try searching. This has been discussed several times before. I don't really mind answering people's questions but there are some here that will flame you to the point where you won't want to come back. Welcome to MacRumors!
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