None of this contradicts the information that I have, but I simply don't have enough information on John to confirm. However, I re-read the letter by Margaret Riddell Biddle to the unnamed sister to see if any of these names lined up. While the sister is still unnamed, she asks "let me know how you all ar and how Mary is and John P.hilly and if Hannah White is married yet".
Now, Mary and Margaret are both fairly common names, but it seems like they could be sisters. The "John P.hilly" could possibly be a Phillip- Margaret's handwriting and spelling are not the greatest. I do not know any connection to Hannah White, perhaps you do?
Finally, at the end of Margaret's letter, she asks her unnamed sister to let her (Margaret) know if "John can walk yet". At first I was confused, but perhaps both sisters had infant sons named John. Did Harriet, Mary or Milacent, to your knowledge, have a young son named John in October 1846?
I will scan and send you the letter referred to ASAP. You might have some better luck deciphering it!