I like
Harriet! :) I never thought of
Hallie as nn for it, but it's definitely a possibility, I think. Personally, I love it with the nn
Hattie. Yes, I do think it's usable today. You might get a few "oh, that's so old sounding" comments at first, but with more Sadies, Isaacs and now Moseses (the plural of
Moses, lol) running around,
Harriet isn't all that far-fetched. And I think
Harriet finishes off your sibset quite nicely. :)
~
Heather~