What a nice surprise to find information about Martha Purdy.I am descended from Lydia (via her daughter, Martha Eliza), and although I was aware of her siblings, Harriet and Darius, I knew nothing of your Martha nor Louisa.
Re: their parentage.I have a copy of Harriet's wedding announcement for her marriage to Edgar McClure in 1892, which states that she is the daughter of Nehemiah and Joann Robinson Purdy. But since there is a big difference in the ages of Lydia and Harriet, I have always wondered if they had the same mother. Lydia had at least four daughters and none of them was named Joann.That surprises me and makes me wonder.
Let me know if you are interested in additional information about Lydia.