Look at each device spec, and note the CPU info, possibly also display and S60/Symbian version info. Then look up from Nokia press releases when a device was announced, and when it started shipping: http://www.nokia.com/press
Once you've worked out which device of a particular display/CPU combo for a particular S60 version, you probably have the "parent device" for that combo (of course, could also be, e.g., the second device instead of the first, if one project caught up and finished before the one that started first).
This approach won't give you the absolute truth, but probably something close enough.
I don't think there's any official published "family tree" of device info that you're looking for.
Re: Nokia Device Families and Parent Devices