[Galadriel55]

So, a few disconnected thoughts, to maybe help the collective effort.

We have 6 iterations of "a [kinsman] to a [kinsman, mostly]". Then there is "a chain of 6 who never met" - begging the connection that it just links all the above statements together, as opposed to a whole separate chain of 6. The difficulty? "The husband to the first" I initially took to mean "the first line/sister/answer" - but that implies a meeting between two answers, it is very hard to be a husband without ever meeting your wife, long-distance relationships aren't popularized in Middle-earth. So perhaps "first" does not, after all, refer to the first line, but to an actual First of some sort.

So what do all the relationship statements have in common? As the only concrete clue we have is the question in the end, my inclination is that they are somehow related to deaths - perhaps actuall killing, or prophecies, or even curses. Actual killings - I have trouble coming up with that many examples of kinslaying in first degree relatives, so probably not. But it does generally put me in mind of the Hurin family and the Gondolin fiasco as potential rich sources for answers. Another instance that comes to mind is Finrod's "I must be free to fulfil my vow" as potentially one of the brother/sister pairs. Were there any good Numenorian child/parent examples? I feel like there ought to be.