[Galadriel55]

I wonder if the directions refer to instructions on a family tree.

If we start with Idril as the first Silver:
1 up are her parents, but as Elenwe's other relations are unknown we are left with Turgon.
1 across is either Fingon or Aredhel.
1 down would be their respective children: Gil-Galad and Maeglin.

But how does 2 down fit it, I am not sure. I thought this would be one of those related-by-multiple-lines things where someone is both a cousin and a cousin once/twice removed, but that doesn't seem to work here.

If Idril is the last Silver, the pathway would still point to a cousin, and the logic still breaks down.

Well, it was worth a try.