Talk About it
On one of my brick wall lines, I realized while talking about it in a lecture on Saturday that there was a first cousin of my great-grandfather who died with no descendants and whose siblings also had no descendants. That meant that the estate would have gone to his first cousins, who in this case may have been spread across the globe. It took talking about the family for this option to "pop" into my head.
Just goes to remind us that talking about a problem (or writing about it) may be enough to get us to notice something that we just keep overlooking when silently studying.