re: question on your page - "is FamilyID really not used ? TODO"
FamilyID in FamilyTable is set via the "Parents" listbox in the Edit Person Fact pane for, events such as Adoption, that have designated parents. The Parents field is normally not visible. Am not sure what else this setting impacts.
Also, the note in Tom's spreadsheet mentions that this is also used for "LDS Seal to Parents" but I don't have any LDS stuff to test with.